Milk
"Best Calcium Source" for Girls?
By Dr. Stephen Walsh
12/16/01
-- Letter to the Editor
Dear BBC
News:
Your article
Milk
'Best Calcium Source' for Girls
contains two serious factual errors, the first being its title.
The overall claim is based on observations by Eastell and others
that many forms of short term calcium supplementation do not result
in sustained gain in bone mineral content or density in children.
This is used as the basis of a claim that milk is the best source
of calcium.
However, the
main evidence for a sustained effect of short-term calcium supplementation
on bone mass comes not from a study on milk supplementation but
from the work of Bonjour et al (Calcium enriched foods and bone
mass growth in prepubertal girls: a randomized, double-blind placebo-controlled
trial, Journal of Clinical Investigation, 1997, 99:1287 -1294 and
A significant effect of calcium enriched foods on bone mineral mass
gain is maintained more than 3 years after discontinuation of intervention,
Journal of Bone Mineral Research, 14, S185). This study used a calcium
phosphate salt derived from milk, and not milk itself, as the supplement.
It therefore indicates that phosphate is important for bone growth
as well as calcium. This is not controversial or novel. Indeed,
calcium phosphate has been used in calcium-fortified soy milks for
many years.
The
claim that cow's milk is specially advantageous for bone growth is
therefore a supposition rather than a deduction from evidence. Bone
health is influenced by many factors, including calcium, protein,
potassium, phosphate, vitamin-D, vitamin-K and magnesium. Up to 10,000
years ago no humans consumed cow's milk yet the archaeological record
shows that our ancestors, in common with our ape relatives, maintained
excellent bone health without having to steal milk from the children
of other mammals to do so. Our ancestral diet, and that of other apes,
includes abundant levels of all the nutrients required for bone health,
drawn overwhelmingly from plant sources. This included about 1500mg
a day of calcium from plant sources such as leaves, shoots, flowers,
nuts and seeds.
The second
serious error in your article is to suggest spinach is a good plant
source of calcium. This is unfortunate as although spinach, like
most dark green leafy vegetables, contains abundant calcium it also
contains exceptional levels of oxalate. The high levels of oxalate
block the absorption of calcium so that only 5% of the calcium is
absorbed, compared to about 30% from cow's milk or fortified soya
milk. In contrast, absorption of calcium from low-oxalate vegetables
such as kale exceeds 50%. A vegan diet including plentiful green
leafy vegetables, such as kale and collards, meets calcium requirements
in a manner consistent with our evolutionary heritage. In addition
such vegetables provide potassium and vitamin-K abundantly and provide
alkali salts that prevent acid from protein causing increased calcium
loss from the body via urine. They also provide abundant folate.
Inadequate folate increases risk of birth defects and cancer.
For those who
are unenthusiastic about the green stuff (beats the white stuff
any day of the week) calcium-fortified soya or pea milks provide
a suitable source of calcium that can be expected to be fully effective
in promoting bone growth. Tofu set with calcium salts also provides
a useful source of calcium, though other forms of tofu do not.
Cow's milk
belongs to calves. We have no need to steal it.
Stephen Walsh
Vice-chair UK Vegan Society
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