Joe,
The problem with beta carotene and vitamin D is that if it is too
low it is just public relations as in golden rice, if it is too
high you face human birth defects...
We are not talking about vitamin D, but vitamin A and the various
carotenoids. And it is not correct to equate Vitamin A with
B-carotene, the principle dietary source of vitamin A activity from
plants. It is B-carotene that was engineered into golden rice (and I
suspect golden potatoes). Birth defects have resulted from high-dose
administration of Vitamin A (retinol) but not from ingestion of large
amounts of carotenoids from plants.
http://www.ingentaconnect.com/searching/Expand?pub=infobike://cabi/pns/1999/00000058/00000002/art00033
Many of our favorite foods are jam-packed with B-carotene, since
carotenoids are accessory pigments in leaves. The carotenoid levels in
many common vegetables are higher than anything you could engineer into
rice or solanum potatoes.
http://www.nutrition.org/cgi/content/full/132/3/506S
The incidence of vit A birth defects was very significant until
pregnant women were advised to avoid vit A supplements...
Some people take very high levels of all sorts of vitamins in the form
of pills, on the mistaken belief that if a little is good, a lot is
better. Extrapolating risk from that dangerous practice to modest
amounts of pro-vitamins in plants is absurd and misleading.
...and to watch their diet for excessive beta carotene. Too little
vitamin A may also cause birth defects so the analogy to goldylocks
porridge may be good.
The amounts of carotenoids that people eat varies tremendously around
the world, yet the body tightly regulates plasma retinol level (unless
you don't eat enough). There is no need to try and regulate this by
adjusting ones diet. Far better to simply eat a whole lot of
vegetables. And the modest amount of B-carotene (less than what is in
carrots) contributed by golden rice or golden potatoes, can only do
good for the millions of people who are deficient in Vitamin A.
Dale
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