the effect of diet on osteoporosis

1. page 16
osteoporosisPresenter: Barbara Hastings-Asatourian,
MSc, BNurs, RN, RHV, RM, Cert. Ed
O
steoporosis generally has no symptoms until a
fracture occurs. People with vertebral fractures may
have back pain, increasing kyphosis or loss of height,
or low-impact wrist fractures. In younger women,
the finding of osteopaenia on routine X-rays may indicate
impending osteoporosis.
The most effective way to diagnose osteoporosis and determine
fracture risk is through testing for Bone Mineral Density. Other
diagnostic tests include urinary calcium measurement, and
spine/ hip x-rays (Wilson 2001). However, this article will
focus not on the diagnostics, but on prevention through
diet (New 2002).
During the teenage years, the sex hormones affect both bone
size and bone strength. By the age of 17, approximately 90% of
the adult bone mass has been established. By 21 years of age
calcium is no longer added to the bones and by 30, loss of
calcium from healthy bones may begin (Woolf 1998).
Girls as young as nine have been found deliberately restricting
essential foods for weight loss. For females, eating enough
calcium is essential during childhood, adolescence, and young
adulthood, when bones achieve their optimum density. Young
persons involved in competitive sports and dancing are
particularly prone to unhealthy dieting. Studies have also shown
that some women smoke to control their appetite. (Maloney et al
1989, Mellin 1988 Trowbridge and Collins 1993),
National nutrition surveys have shown that many women and
young girls consume less than half the recommended amount
of calcium needed for growing and maintaining healthy bones.
Table One illustrates calcium contents of a selection of easily
accessible foods.
In the second
part of our focus
on osteoporosis,
we look at the
effect of diet on
the condition
As well as the dietary sources listed, drinking water in hard water areas
has been found to be rich in calcium. It has been one public health
consideration that addition of calcium to drinking water may have
beneficial effects on bone.
When diet is low in calcium, supplementary calcium is recommended.
There have been two interesting recent findings about calcium
supplements. Firstly, when calcium enriched mineral water is taken in
small amounts throughout the day calcium is efficiently absorbed.
Secondly, twice daily smaller half doses of calcium supplements are
more effective in maintaining calcium levels than taking one large
dose once daily (New 2002).
fluoride
Although not yet licensed in the UK as a supplement for osteoporosis
prevention, the addition of fluoride salts to drinking water has been
shown in some international studies to have a positive effect on
spinal and femoral neck bone mass. (Food and Nutrition Board of the
Institute of Medicine 1997)
dieting
Childhood and adolescence are the most important times to ensure
adequate calcium intake. There is evidence that young girls and
teenagers are the most deficient in calcium and vitamin D. Efforts to
promote heart health have emphasised the positive aspects of
skimmed milk but have failed to highlight the need for fat-soluble
vitamins. Low fat milk may have increased calcium, but lacks these
vitamins. Teenagers often cut out dairy products because they consider
them too fatty. Milk is a good source of calcium and teenagers often
fail to make up the amount lost through other food. Weight loss has
been shown to be associated with increased bone reabsorption, as
necessary calcium is taken from the bones in the absence of sufficient
amounts in the diet (Trowbridge and Collins 1993).

2. eating disorders
Eating disorders often start in adolescence and
more than 90% of anorexia and bulimia cases
occur among females. Anorexia nervosa
and bulimia nervosa affect as many 3% as of
adolescent and young adult females, a figure
which appears to be increasing.
Eating disorders and over-exercise syndrome may
result in suppression of oestrogen levels and
amenorrhoea if weight loss results in a body mass
index (BMI) of less than 19. This in turn may
impair the achievement of peak bone mass and
cause early bone loss. In one Danish study,
subjects with anorexia and bulimia were found to
be two to three times more likely to suffer a
fracture than subjects without an eating disorder.
The consequent increased fracture risks persisted
for up to 10 years after diagnosis and treatment
(Beals and Manore 1994, Herzog and Copeland
1985, Mellin 1988).
vitamin D
Vitamin D is a fat-soluble vitamin that enables
calcium to transfer from intestine to bloodstream
and prevents excretion of calcium in the urine.
Without sufficiant vitamin D the body begins to
draw calcium from bones.
Food sources of vitamin D include dairy
products, egg yolks, oily fish and liver. The
recommended daily intake is 400 – 800
international units (DoH 1998).
Vitamin D is also derived from exposure of
the skin to solar ultraviolet B radiation. It is
manufactured in the skin following direct
exposure to sunlight. Studies recommend that
10-15 minutes exposure of hands, arms and face
two to three times a week is normally enough,
but the efficiency of this mechanism is also
dependent on the time of day, season, latitude,
skin pigmentation, skin sensitivity, pollution levels
and sunscreens.
There is evidence of significant problems in
population groups who restrict their skin exposure
for cultural and religious reasons. Dress covering
the whole body has adverse effects on vitamin D
status and the potential for causing secondary
hyperparathyroidism in the long term.
Dark winter months in northern latitudes also
increase the risk of vitamin D deficiency and
consequent bone loss. One small German study of
a group of 10 men and 20 women found that
low-dose supplementation with 500 mg of
calcium per day and 500 IU of vitamin D per day
during the winter months effectively prevented
bone loss.
Sunscreen markedly diminishes the manufacture
of vitamin D in the skin, as do window glass,
clothing and air pollution. Skin colour also affects
vitamin D production: the fairer the skin, the
more vitamin D is manufactured. (Compston
1998, Malabana et al 1998)
fitness network
page 17
fn
part 2
food serving size calcium content mg
Skimmed milk: One glass (300g) 360
Cheddar cheese: 50g 360
Semi-skimmed milk: One glass (300g) 354
Whole milk: One glass (300g) 345
Plain yoghurt: One pot (150g) 285
Tinned sardines: 50g 275
Dried figs: Four (80g) 200
Vanilla ice cream: Two scoops 144
Plain fromage frais: 100g 89
Baked Beans: 135g 72
Sesame seeds: 10g 67
Almonds: 25g 60
Tinned salmon: 50g 47
Watercress: 20g 34
White bread: One large slice 33
Wholemeal bread: One large slice 19
Broccoli: 45g 18
Peanuts: 25g 15
(Source: DoH 1998)
Birth to six months 210
Six months to one year 270
One to three years 500
Four to eight years 800
Nine to 13 years 1300
14-18 years 1300
19-30 years 1000
1-70 years 1200
71 and over 1200
references
Compston JE. Vitamin D
deficiency: time for action.
Br Med J. 1998;317: 1466-1467.
Malabana A, Veronikis IE,
Holick MF. Redefining vitamin
D insufficiency. Lancet.
1998;351:805-806
Ghatge KD, Lambert HL, Barker
ME, Eastell R. Bone mineral gain
following calcium supplementation
in teenage girls is reversed two
years after withdrawal of the
supplement. J Bone Miner Res.
2001;16(suppl 1):S173.
Food and Nutrition Board of the
Institute of Medicine. Dietary
Reference Intakes: Calcium,
Phosphorus, Magnesium, Vitamin
D and Fluoride. Washington, DC:
National Academy Press; 1997.
table 1: dietry sources of calcium
table 2: recommended intake
of calcium mg / day