Bone Appétit

24 Pages·2006·1.07 MB·English

Invest in your bones
Bone Appétit
The role of food and nutrition in building
and maintaining strong bones
Written on behalf of the IOF Committee of Scientific Advisors by Bess Dawson-Hughes, MD, Professor of Medicine, Director
of the Bone Metabolism Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, and Director of the
Metabolic Bone Diseases Clinic, Tufts-New England Medical Center, Tufts University, Boston, MA, USA. Prof Dawson-Hughes
is an IOF Board member, and a member of the Board of Trustees of the National Osteoporosis Foundation, USA.
IInntteerrnnaattiioonnaall OOsstteeooppoorroossiiss FFoouunnddaattiioonn membership has more than doubled since
1999, reflecting the increasing international
IOF is an international non-governmental concern about this serious health problem.
organization which represents a global There are 173 member societies in more
alliance of patient, medical and research than 80 locations worldwide (June 2006).
societies, scientists, health care professionals
and the health industry. IOF works in part- For more information about IOF and to
nership with its members and other organi- contact an IOF member society in your
zations around the world to increase aware- country visit: www.osteofound.org
ness and improve prevention, early diagno-
sis and treatment of osteoporosis. Although IOF
osteoporosis affects millions of people Rue Juste-Olivier 9
everywhere, awareness about the disease is CH-1260 Nyon
still low, doctors often fail to diagnose it, Switzerland
diagnostic equipment is often scarce, or not Tel: [phone]
used to its full potential, and treatment is [email protected]
not always accessible to those who need it www.osteofound.org
to prevent the first fracture. IOF’s growing
WWhhaatt iis oosstteeooppoorroossiiss?? progressively over many years and doesn’t
have any symptoms, and often the first sign
Osteoporosis is a disease in which the densi- of having osteoporosis is a fracture. For this
ty and quality of bone are reduced, leading reason, osteoporosis is often referred to as
to weakness of the skeleton and increased the “silent epidemic”.
risk of fracture, particularly of the spine, hip
and wrist. Osteoporosis is a global public Osteoporosis currently affects approxi-
health problem; the disease and its associat- mately one in three women and one in five
ed fractures are an important cause of men over the age of 50 years, and is increas-
morbidity and mortality affecting millions of ing in significance as the population of the
people worldwide. The loss of bone occurs world grows in size and is living longer
The number of hip fractures occurring
worldwide each year is expected to rise
from the current figure of over 1.5 million
to over 6 million by the year 2050, with the
steepest increases expected throughout Asia
and Latin America1
Having a spine fracture substantially
increases the risk for sustaining additional
spine fractures within one year2
Every 30 seconds, someone in the
European Union has an osteoporotic
fracture3
For the elderly who survive a hip fracture,
only one in three returns to their previous
level of independence4
Normal bone Osteoporotic bone
1
Foreword
World Osteoporosis Day this year, 2006, celebrates the theme of food and
nutrition, which marks the middle year of the IOF’s global, 3-year ‘lifestyle’
campaign. I use the word ‘celebrates’ with good reason – food is not just ‘fuel’
for the body, but is one of the joys of life, for all its associated tastes, textures,
sights and scents, and for the pleasures it brings in allowing shared time with
family and friends. Last year’s theme was exercise-oriented, with the admonish-
ment to ‘Move it or Lose it’, and next year we will cover the whole gamut of
osteoporosis risk factors under the theme ‘Beat the Break – know and reduce your risks’. However, for
this year, we offer a respite from all the cautions, and invite you to do more of something pleasurable –
include more calcium-, vitamin D- and protein-rich foods and drinks in your diet, and give your bones
the boost they need to last you a lifetime.
A healthy, nutritious diet is one of the cornerstones of ensuring strong, healthy bones at every stage in
life. Certainly, during childhood and adolescence, good nutrition will help to ensure attainment of
maximal peak bone mass, and thereby reduce vulnerability to osteoporosis later in life. However, the
phrase ‘never too late’ is highly appropriate for bones – a healthy diet is also extremely important for
preserving bone mass and strength both in younger and older adults, even in those who have already
had a fracture – good nutrition speeds and aids recovery, and helps prevent further fractures. This
review, for which I would like to acknowledge the co-authorship of Dr Jo Cadogan at the IOF, covers
the scientific basis for many of the claims made regarding nutrition and bone health, and also covers
some of the ‘negative’ dietary factors and practices.
Good nutrition alone will neither prevent nor cure osteoporosis, but in the context of measures to
ensure a bone-friendly lifestyle – including avoiding smoking and excess alcohol, and taking exercise –
it is perhaps the least onerous task on the list. Bone Appétit!
Bess Dawson-Hughes, MD
Professor of Medicine,Tufts-New England Medical Center, Tufts University, Boston, MA, USA
2
Introduction
B
one is a living, dynamic, metabolically active tissue –
throughout the whole of life. Bone is made up of two
major types: cortical bone, which forms the hard, smooth
outer shell of the bones, and trabecular bone, which is
inside the bones and has a honeycomb-like structure. Bone
undergoes a process of constant renewal throughout life,
through a process called bone turnoverin which cells
called osteoclasts remove old or damaged bone, and cells
called osteoblasts make new bone to replace it. Bones can
also adapt their ‘architecture’ to the demands of different
activities, such as a new type of exercise. Bone is a special-
ized connective tissue, composed of a collagen (protein)
framework permeated with mineral salts composed of
mostly calcium and phosphate, together with trace
amounts of other minerals and ions. Just like the muscles, will help to slow the rate of bone tissue thinning and
the heart and any other organ in the body, the skeleton reduce the risk of having osteoporosis-related fractures,
needs a constant supply of energy and nutrients. A healthy, for both men and women.
balanced diet containing both macronutrients (protein, fat
and carbohydrate) and micronutrients (vitamins and min- The mineral calcium is one of the major building blocks
erals), plus sufficient calories, is vital for both the normal for the skeleton, and is essential for bone health through-
development and on-going maintenance of the skeleton. out life. Vitamin D is also essential for the development
and maintenance of bone, both for its role in assisting
The critical years for building bone mass are during child- calcium absorption from the diet, and for ensuring the
hood and adolescence. This is when new bone is formed proper renewal and mineralization of bone tissue. Protein
more quickly than old bone is removed, causing bones to is also a key constituent of bone tissue and therefore an
become larger and denser. This pace continues until adequate dietary supply is essential. By investing in the
around the mid 20’s when ‘peak bone mass’ is normally ‘bone bank’ during youth and early adulthood, through
reached (maximum bone density). Bone tissue loss general- good nutrition and lifestyle, the bones become stronger
ly begins after the age of about 40 years, when we are no and less vulnerable to osteoporosis later in life. Short-term
longer able to replace bone tissue as quickly as we lose it. studies in children and teenagers suggest that a higher
In women, the rate of bone tissue loss increases quite sub- calcium or dairy intake is associated with enhanced bone
stantially in the few years immediately after menopause, mineral gain. If the higher intakes were to be maintained
when estrogen production stops and bones no longer ben- into young adulthood, it is likely that this would have a
efit from its protective effect. Men also suffer from loss of positive impact on peak bone mass.
bone tissue after age 50 years, but the rate of loss is slow-
er than in women. At this stage in life, taking preventive Good nutrition, especially protein, calcium and vitamin D,
measures – including ensuring a balanced, healthy diet – is also important for preserving bone mass and strength in
Bone mass changes throughout life,
showing effect of low peak bone mass,
Optimal peak or higher rate of bone loss
This hypothetical graph is a representation of bone mass
changes throughout life. The critical years for building
bone mass are during childhood and adolescence. ‘Peak
s bone mass’ is achieved in the mid-20’s, then bone mass
s
a remains stable during young adulthood. Bone loss begins
m after the age of about 40 in both genders.
e Low peak
n
o The graph also shows two hypothetical situations, one in
B Higher which a low peak bone mass is attained (gray, dashed),
rate of loss Fracture and one in which bone loss is faster than it should be
(green, dotted). In both situations, this would place a person
risk zone
at risk of fracture at an earlier age in life, i.e. they would
enter the shaded ‘fracture risk zone’ sooner. Healthy
lifestyle habits, including good nutrition and exercise, can
0 10 20 30 40 50 60 70 80 help to ensure that individuals attain their maximum peak
Age (years) bone mass, and also help to slow bone loss, ensuring they
stay on the optimum (blue, solid) line in life.
3
adults and the elderly. In addition, attention to nutrition is
an important component of a successful rehabilitation pro- Nutritional factors
gram in patients who have had an osteoporotic fracture.
In frail, elderly patients who have sustained hip fractures
this is crucially important, as poor nutritional status can and bone health
slow recovery, and increase susceptibility to further
fractures.
Comparisons between parents and their children, or Calcium and vitamin D
between twins, suggest that genetics accounts for 60 to
80% of the variability in bone mineral density (BMD)
between individuals. However, although genetic factors are The two key nutrients to consider for bone health are the
very important in determining whether an individual is at mineral calcium, and vitamin D. Calcium is a major
heightened risk of osteoporosis, lifestyle factors such as structural component of bone tissue. It is deposited in
good nutrition and exercise play a key role in building bone in the form of a mineral complex called hydroxyap-
bone during youth, maintaining bone mass in younger atite, which confers strength to the skeleton. Ninety-nine
adults, and helping to slow down bone loss in adults and percent of the calcium in the body is stored in the skele-
the elderly. The importance of these lifestyle factors is that ton, which therefore also acts as a ‘reservoir’ of calcium
they are amenable to change (unlike your genes) – for maintaining calcium levels in the blood. Blood calcium
individuals can take positive steps to strengthen their levels have to be tightly maintained at a constant level, for
bones and reduce their risk of osteoporosis. calcium’s other roles such as in nerve and muscle function-
ing. Recommended daily calcium intakes for populations
vary between countries, often as a result of differing use
and interpretation of the available scientific data. The
FAO/WHO5recommendations, based on data from
several countries, are shown in Table 1.
Good nutritional habits, which
Calcium is absorbed in the small intestine both by passive
begin early in life, will help to
diffusion, and by an active mechanism which requires vita-
promote bone health over the min D. An inadequate intake of calcium results in a reduced
whole lifetime. amount of calcium being absorbed, which in turn leads to a
lower blood level of calcium. As a result our bodies produce
a hormone, called parathyroid hormone (PTH) that causes
calcium to be released from the bone ‘reservoir’ into the
blood stream, because as stated above it is vital that blood
calcium levels are kept constant at all times. It is thought
that if calcium intake is habitually low on an ongoing basis
(over years), then the small but sustained increase in the
PTH level over time could cause a gradual loss of calcium
from the bones, making them thinner and weaker.
Calcium requirements are high in the teenage years, during
the time of rapid growth of the skeleton, and during this
time, calcium absorption efficiency increases. The efficien-
cy of calcium absorption, however, declines with age. This
means that over time we need to consume higher amounts
of calcium, which is why higher intakes are usually recom-
mended for people over 65 years. We must also ensure
that we have enough vitamin D (via sunlight exposure or
dietary intake), to help with the process of calcium
absorption. Diet composition, season and race also
influence calcium absorption efficiency.
Milk and other dairy foods are the most readily available
sources of calcium in the diet. Dairy foods have the addi-
tional advantage of being good sources of protein and
other micronutrients (besides calcium) that are important
for bone and general health. Other good food sources of
calcium include certain green vegetables (e.g. broccoli,
curly kale, bok choy); whole canned fish with soft, edible
bones such as sardines or pilchards; nuts (almonds and
Brazil nuts in particular); and tofu set with calcium.
4
Although some other plant foods also contain appreciable called ‘soy milk’, but it is important to look for ones that
amounts of calcium, some contain substances that bind to are fortified with calcium, because soy drinks don’t natu-
the calcium and prevent it being absorbed, e.g. compounds rally contain calcium. Some examples of the approximate
called oxalates in spinach and rhubarb, and phytates in calcium levels in foods7are shown in Table 2.
dried beans, cereal husks and seeds6. However, oxalates
and phytates only bind the calcium in the foods they are in Vitamin D is also essential for the development and main-
– they don’t interfere with calcium absorption from other tenance of bone, both for its role in assisting calcium
foods or drinks. Calcium-fortified foods and drinks, absorption from food in the intestine, and for ensuring the
including breads, cereals, orange juice and soy beverages correct renewal and mineralization of bone tissue.
are also available in some countries, as are various com- Vitamin D is made in the skin when it is exposed to
mercial brands of mineral waters which can contain signif- sunlight (ultraviolet B rays); in children and adults expo-
icant amounts of calcium. Soy beverages are sometimes sure of the hands, face and arms to the sun for as little as
10 to 15 minutes per day is usually sufficient for most
individuals. Vitamin D can also be obtained from food,
and dietary supplements. Food sources of vitamin D are
rather limited, and include oily fish such as salmon,
sardines and mackerel, eggs, liver, and in some countries
fortified foods such as margarine, dairy foods and cereals
(Table 3). The version of vitamin D made in the skin is
referred to as vitamin D (cholecalciferol), whereas the
3
dietary form can be vitamin D or a closely related mole-
3
cule of plant origin known as vitamin D (ergocalciferol).
2
The vitamin D compound that is measured in the blood,
to test whether a person has adequate vitamin D status, is
called 25-hydroxyvitamin D. However, this is not the
‘active’ form of vitamin D (the form that promotes intes-
Table 2: Approximate calcium levels in foods
Food Serving size Calcium (mg)
Milk,whole 236 ml / 8 fl oz 278
Milk,semi-skimmed 236 ml / 8 fl oz 283
Milk,skimmed 236 ml / 8 fl oz 288
Goats milk,pasteurized 236 ml / 8 fl oz 236
Yoghurt,low fat,plain 150 g / 5 oz 243
Table 1: Recommended calcium allowances* (mg/day) Yoghurt,low fat,fruit 150 g / 5 oz 210
Yoghurt,Greek style,plain 150 g / 5 oz 189
Infants and children: Fromage frais,fruit 100 g / 3.5 oz 86
0-6 months 300-400 Cream,single 15 g / 1 tablespoon 13
7-12 months 400 Cheese,cheddar type 40 g / medium chunk 296
1-3 years 500 Cheese,cottage 112 g / 4 oz 142
4-6 years 600 Cheese,mozzarella 28 g / 1 oz 101
7-9 years 700 Cheese,Camembert 40 g / average portion 94
Adolescents: Ice cream,dairy,vanilla 75 g / average serving 75
10 to 18 years 1300** Tofu,soya bean,steamed 100 g / 3.5 oz 510
Women: Soya drink 236 ml / 8 fl oz 31
19 years to menopause 1000 Soya drink,calcium-enriched 236 ml / 8 fl oz 210
Postmenopause 1300 Broccoli,cooked 112 g / 4 oz 45
During pregnancy (last trimester) 1200 Curley kale,cooked 112 g / 4 oz 168
Lactation 1000 Apricots,raw,stone removed 160 g / 4 fruit 117
Men: Orange,peeled 160 g / 1 fruit 75
19-65 years 1000 Figs,ready to eat 220 g / 4 fruit 506
65+ years 1300 Almonds 26 g / 12 whole 62
Brazil nuts 20 g / 6 whole 34
*The ‘recommended allowance’ refers to the amount of calcium that each age Sardines,canned in oil 100 g / 4 sardines 500
group is advised to consume (with daily intake corresponding to an average Pilchards,canned in tomato sauce 110 g / 2 pilchards 275
intake over a period of time),to ensure that calcium consumed compensates for Whitebait,fried 80g / average portion 688
calcium excreted from the body each day (e.g.in the urine),and lost in other Bread,white,sliced 30 g / 1 medium slice 53
ways (e.g.through the skin,hair and nails). The calcium allowance figures for Bread,wholemeal,sliced 30 g / 1 medium slice 32
children and adolescents also take account of skeletal growth (net calcium gain), Pasta,plain,cooked 230 g / medium portion 85
and those for postmenopausal women and the elderly also take account of a Rice,white,basmati,boiled 180 g / medium portion 32
lower intestinal calcium absorption efficiency.
**Particularly during the growth spurt.
Calcium levels from reference 7: Food Standards Agency (2002) McCance and
Figures based on Western European,American and Canadian data.Source: Widdowson’s The Composition of Foods,Sixth summary edition.Cambridge:
FAO/WHO:Human Vitamin and Mineral Requirements,2002,reference 5. Royal Society of Chemistry.
5
tinal calcium absorption); the kidney converts 25-hydroxy-
vitamin D into the active form, which is called 1,25-dihy-
droxyvitamin D, according to the body’s requirements
(e.g. if calcium intake is low, more 1,25-dihydroxy-
vitamin D is produced, to enhance calcium absorption).
Because the sun provides a source of vitamin D in varying
amounts for different individuals, dietary recommenda-
tions for vitamin D are approximate. Many countries
advise a dietary intake of 200 IU/day (5 µg/day) for chil-
dren and young adults, and 400-600 IU/day (10-15 µg/day)
for older persons, to augment that derived via sun expo-
sure. The FAO/WHO5dietary intake recommendations are
shown in Table 4. These recommendations are derived
from calculations of the intakes required to achieve an
optimal blood level of vitamin D, together with various
other factors. There is as yet no common definition of
‘optimum’ vitamin D status, although there is emerging
evidence and expert opinion that the minimum blood level
of 25-hydroxyvitamin D that would be optimal for frac-
ture prevention is 70-80 nmol/l8. To achieve this, an aver-
age older man or woman would need a vitamin D intake
of at least 800-1000 IU/day (20-25 µg/day), which is
approximately double the intake recommended in most
countries.
Dietary or supplemental vitamin D increases in importance
during the winter months for populations in northern lati-
tudes (when no skin synthesis of vitamin D takes place),
and for elderly people who do not go outdoors much and
in whom the capacity for skin synthesis of vitamin D is
Vitamin D is made in the skin on exposure
reduced. Use of sunscreen creams, and a greater degree of
to the sun’s ultraviolet B rays. Casual
skin pigmentation, also reduces the amount of vitamin D
that is made in the skin. An increasing body of evidence exposure of the face, arms and hands for as
suggests that on a global level, vitamin D deficiency is little as 10 to 15 minutes per day is
widespread, even in very sunny countries such as in the
usually sufficient for most individuals.
Middle East and parts of Australasia9.
Table 3: Approximate vitamin D levels in foods
Food µg per IU per % RNI (10 µg/d
serving serving or 400 IU/d)*
Cod liver oil**,1 tbsp 23.1 924 231
Salmon,grilled,100g 7.1 284 71
Mackerel,grilled,100g 8.8 352 88 Table 4: Recommended vitamin D intake
Tuna,canned in brine,100g 3.6 144 36 by age group, both as international units (IU) and micrograms (µg) per day
Sardines,canned in brine,100g 4.6 184 46
Margarine,fortified,20g 1.6 62 16 Age group RNI*(IU/d) RNI (µg/d)
Bran Flakes***,average serving,30g 1.3 52 13 0-9 years 200 5
Egg,hen,average size,50g 0.9 36 9 10-18 years 200 5
Liver,lamb,fried,100g 0.9 36 9 19-50 years 200 5
51-65 years 400 10
*The RNI (recommended nutrient intake) for adults,ages 51-65 years. The RNI is 65+ years 600 15
defined by the FAO/WHO as “the daily intake which meets the nutrient requirements Pregnancy 200 5
of almost all (97.5%) apparently healthy individuals in an age- and sex-specific Lactation 200 5
population group”.Daily intake corresponds to the average over a period of time.
**Fish liver oils,such as cod liver oil and halibut liver oil,also contain Figures based on Western European,American and Canadian data.Source:
appreciable amounts of vitamin A,which can be toxic if consumed in excess. FAO/WHO:Human Vitamin and Mineral Requirements,2002,reference 5.
***Bran Flakes are given as an example of a vitamin D-fortified breakfast cereal.
*The RNI (Recommended Nutrient Intake) is defined by the FAO/WHO as
From reference 7:Food Standards Agency (2002) McCance and Widdowson’s The “the daily intake which meets the nutrient requirements of almost all (97.5%)
Composition of Foods,Sixth summary edition.Cambridge:Royal Society of apparently healthy individuals in an age- and sex-specific population group”.
Chemistry. Daily intake corresponds to the average over a period of time.
6
Vitamin D insufficiency
is widespread
Increasingly, scientific evidence 100
D
svuitgagmeisnt sD t hinastu offni caie gnlcoyb iasl wleivdeel-, n 90
spread, even in very sunny mi%) 80 81%
regions such as the Middle East, a( 70
Ltraiteisn, aAnmde Ariucastnr aalniad. TAhsiias nis ccoleuanr-- of vitency 6500 59% 63% 59%
ltyio dneaml eopnisdteramteiodl oing itchails s itnutdeyr nina- ce fici 40 51% 52%
nf
postmenopausal women. The eu 30
prevalence of vitamin D inade- alns 20
quacy was over 50% in all five vi
world regions, and was highest re 10
P
in the Middle East (81%) and 0
Asia (63%). All Latin America Europe Middle East Asia Australia
Regions
Global prevalence of low serum 25(OH)D levels (defined as < 30 ng/ml).
Cross-sectional observational international study in 1,285 community-dwelling,
postmenopausal women with osteoporosis, in 18 countries (from reference 9).
In children, severe vitamin D deficiency results in inade- tine, which in turns leads to higher PTH levels and greater
quate mineralization of the bone matrix, leading to calcium loss from the bones. Over time this leads to bone
growth retardation and bone deformities known as rickets. loss and eventually osteoporosis. Poor vitamin D status in
In adults, the same condition is known as osteomalacia older adults and the elderly also increases the likelihood of
(‘softening’ of the bones, due to the poor mineralization). falling (and therefore possibly sustaining a fracture),
In industrialised countries, rickets and osteomalacia are because vitamin D is also important for the correct func-
relatively rare conditions. However, milder degrees of tioning of the muscles and nervous system10. Maintaining
vitamin D inadequacy are common, and can predispose to adequate vitamin D status during pregnancy is important,
osteoporosis. This is because without a sufficient supply of as there is some evidence that mothers deficient in 25-
vitamin D from the skin or diet, the metabolism of hydroxyvitamin D in pregnancy give birth to children with
calcium is disturbed. For example, lower vitamin D levels reduced bone mass, which could in turn be a risk factor
result in less efficient calcium absorption from the intes- for osteoporosis later in life11.
The best dietary source of
vitamin D is oily fish (also
called fatty fish). A portion
of an oily fish such as
salmon, tuna, sardines or
mackerel provides a good
amount of vitamin D, up to
a half or two-thirds of our
daily recommended intake.
7
The effects of calcium, vitamin D In studies among adults, one three-year intervention study
in healthy young women aged 30-42 years showed that
and dairy foods on bone density
supplementing the usual diet with dairy foods prevented
and fracture risk bone loss in the spine, compared with control subjects
who did not increase their dietary calcium intake17. In
The importance of nutrition to bone health has been postmenopausal women and the elderly, several interven-
demonstrated in a number of research studies, in human tion studies have shown that calcium or milk supplemen-
subjects across the age range. Intervention trials carried tation slows the rate of bone loss18-27. In a study carried
out over one to three years in children and adolescents out in healthy, elderly women living in nursing homes,
have shown that supplementation with either calcium, calcium (1200 mg/day) and vitamin D (800 IU/day)
dairy calcium-enriched foods, liquid milk, or a calcium- supplementation over 18 months reduced the risk of hip
enriched milk powder enhances the rate of bone mineral fractures and other non-vertebral fractures19. A similar
acquisition, compared with un-supplemented (or placebo) intervention over three years (500 mg/day calcium, 700
control groups12-15. In general, these trials increased the IU/day vitamin D) was shown to reduce bone loss and the
usual calcium intake of the supplemented children from incidence of non-vertebral fractures in elderly men and
about 600-800 mg/day, to around 1000-1300 mg/day. women living at home, i.e. not in institutions18. In compar-
Although these studies were short term, if the higher ative intervention studies, dairy food supplements and
calcium intakes were maintained into the mid-20’s, such calcium supplements were equally effective in preserving
an increment would likely have a beneficial impact on hip bone mass in postmenopausal women24,27, although
peak bone mass. Some retrospective observational studies these studies were not designed to evaluate reductions in
suggested that adults who consumed milk regularly during fracture rates. Several studies have shown that vitamin D
childhood had a higher bone mass than those who did alone and in combination with calcium lowers the risk of
not, although such studies are a weaker form of scientific falling in older men and women8.
evidence than intervention trials. At the population level,
it is estimated that a 10% increase in peak bone mass
could reduce the risk of osteoporotic fractures during
adult life by 50%16.
Explanation of study designs
Observational studies
In observational studies, nothing is given to the study
Throughout this report, several different types of studies participants. Instead, as the name implies, they are
investigating effects of nutrition on bone health are ‘observed’ in the course of their normal life. A simple
described. When evaluating scientific evidence, it is example is a cross-sectional study, e.g. where you might
important to take into account the type of study, as some take a group of people, measure their calcium intake on
provide ‘stronger’ evidence than others. Broadly, studies one occasion with a questionnaire, measure their bone
are classified as either an ‘intervention trial (study)’ or an density, and investigate statistically to see if calcium
‘observational study’. Sometimes observational studies are intake correlates (shows a relationship) with bone density.
broadly referred to as ‘epidemiological studies’. Another, stronger type of observational study is the
prospective cohort study, in which a large group (cohort)
Intervention trials of people is studied over a long period of time, usually
Also called clinical trials, these are the ‘gold standard’ in years (hence ‘prospective’), and investigators can look at
study design, providing the strongest type of scientific how their dietary intake affects measures of disease
evidence. The best design is the randomised, double- outcome (e.g. fractures). Usually the investigators divide
blind, placebo-controlled intervention trial. The partici- the cohort into 3, 4 or 5 groups (tertiles, quartiles or
pants are randomly (like tossing a coin) allocated to two quintiles) according to low, medium and high intake of a
groups, one group being the ‘intervention’ group who particular food or nutrient, and compare the bone densi-
will receive the treatment item to be tested (e.g. a calci- ties or fracture rates between the groups. Well-known
um tablet, or a medicine in a drug trial), and the other examples of this type of design are the Nurses Health
group being the ‘control’ (comparison) group, who will Study and the Framingham study in the USA, which
receive a placebo (dummy) tablet. ‘Double-blind’ refers to involve thousands of study subjects. It is also possible to
the fact that neither the investigators nor the subjects look back in time, at people’s previous diet or ‘exposure’,
know which tablet – treatment or placebo – they are and how it affects their current disease risk. Examples
receiving. Therefore, the only difference between the two include retrospective cohort studies, and case-control
groups is whether or not they receive the treatment, and studies. The latter compare ‘cases’ (people who have the
the investigators can then see whether it changes bone disease) with ‘controls’ (people free of the disease), and
mineral density (as an example of a ‘study outcome’) over looks at whether measures of dietary exposure
a period of time. If a food is used as the intervention (e.g. statistically ‘predict’ the disease outcome.
milk), it is not possible for the study to be double-blind or
placebo-controlled, so it would be called a ‘randomised,
controlled, open, intervention trial’.
8
The above-described trials demonstrated the effectiveness Calcium and vitamin D alone are insufficient to prevent
of calcium and vitamin D supplementation for reducing the rapid bone loss that occurs in women around the time
non-vertebral fracture rates in at-risk populations, such as of the menopause, or to reduce fracture risk optimally in
men and women over 65 years, and elderly living in care patients with osteoporosis. Nevertheless, they are an essen-
homes. Other trials carried out in adults living at home tial component of therapy, in patients diagnosed with
(i.e. not in care homes) have not shown a benefit of calci- osteoporosis. It is recommended that people of all ages
um and vitamin D supplementation in terms of fracture ensure adequate intakes in order to keep bones as strong
prevention. One such study is the Women’s Health and healthy as possible. Dairy foods provide the most
Initiative (WHI) calcium plus vitamin D trial, a large readily available dietary sources of calcium, and also
placebo-controlled intervention trial carried out in improve the nutritional quality of the diet in other respects
American women ages 50-79 years, which showed no because they contain protein and an array of vitamins and
apparent benefit of calcium with vitamin D supplementa- minerals30,31. It is sometimes stated in the lay press that
tion on fracture rates in the supplemented group as a dairy foods might be detrimental to bone health, based on
whole over seven years, compared with the placebo the observation that the countries with the highest dairy
group28. However, hip fracture rates weresignificantly food intakes (and also in consequence, the highest calcium
reduced by 30%, both in women who used only the intakes) have the highest rates of osteoporotic fractures.
calcium and vitamin D supplements provided in the study However, this argument is confounded by the fact that
(meaning that they had the lowest habitual calcium and these tend to also be the countries with the longest life
vitamin D intakes, because they weren’t already taking expectancies, and age is the strongest risk factor for osteo-
their own supplements), and in those who were compliant porosis – the longer you live, the more likely you are to
with the supplements (defined as those who took at least have a fracture. In addition, it is highly problematic
80% of their calcium and vitamin D). A further explana- making comparisons of disease rates between countries,
tion for the negative finding in the whole group could be due to variations in other factors such as racial and
that the dose of vitamin D used (400 IU/day) was not genetic differences, physical activity levels, total dietary
sufficient, since it appears that supplementation of 700 or patterns, sun exposure, disease reporting accuracy, and
800 IU/day is needed to reduce the risk of hip and other many other population-level differences. Another argu-
fractures29. ment leveled against dairy foods is that they are high in
Special considerations for calcium and vitamin D in the elderly
Elderly persons are at increased risk for calcium and vitamin D insufficiency. There are also several alterations in body
functions that can contribute to calcium loss from bone, and hence increased risk of osteoporosis.
With ageing there is:
A decrease in dietary calcium intake, usually as a
result of decreased overall dietary energy intake
(e.g. poorer appetite, intercurrent
illnesses, social and economic factors)
A decrease in the intestinal absorption of
calcium (exacerbated if vitamin D status is low)
A decrease in the capacity of the intestinal cells
to adapt to a low calcium intake, and increase their
absorptive capacity
Less frequent exposure to sunlight (e.g. elderly
who are housebound, or institutionalized, or have
reduced mobility), hence poorer vitamin D status
A decrease in the capacity of the skin to
synthesize vitamin D
A decrease in the efficiency with which the
kidneys can retain calcium, leading to increased
calcium loss in the urine
A decrease in the capacity of the kidneys to
convert vitamin D into the most active form,
1,25-dihydroxyvitamin D