"The scientists contacted over 8,000 men and women aged 30 who were born in April 1970 and had had their IQ tested at age 10 because they were part of the 1970 British Cohort Study. They found a strong link between high IQ at age 10 and having a vegetarian diet at age 30."
Iodine is typically undesirably low (about 50mcg per day compared to a recommended level of about 150mcg) in vegan diets unless supplements, iodine-rich seaweeds or foods containing such seaweeds are consumed. The low iodine levels in many plant foods reflect the low iodine levels in the soil. About half the iodine consumption of omnivores comes from dairy products.
In October of 2003, one of many articles appeared on iodine deficiency in vegetarians and vegans [Annals of Nutrition and Metabolism 47 (2003): p.183]. Quoting from the paper: "One fourth of the vegetarians and 80% of the vegans suffer from iodine deficiency..." Only 9% of the meat-eaters were deficient.
Vitamin B12 deficiency is the most common cause of megaloblastic anemia. Both long-term low dietary consumption and poor absorption are responsible for the final outcome of a B12 deficiency, namely megaloblastic anemia and neurological symptoms.
The authors of one study note that the vegan diet provides essentially no vitamin B12, and people following unsupplemented vegetarian diets may suffer from a deficit as well due to the lower levels in the diet. In addition, people consuming the vegan and vegetarian diets were in general also not getting adequate amounts of the essential amino acid methionine, due to the lower methionine content in plant proteins versus animal proteins. [Annals of Nutrition and Metabolism 2000;44: pp.135-8]
Serum vitamin B12 levels were 37% lower in the vegetarian group and 59% lower in the vegan group, compared with the omnivorous group. Serum B12 levels:
In addition, B12 levels were low enough to be considered clinically deficient in:
* 78% of the vegans
* 26% of the vegetarians
* 0% of the omnivores
Researchers compared homocysteine (Hcy) levels in 62 vegetarians, 32 vegans, and 59 people consuming an omnivorous diet. Compared to the omnivorous group, whose average Hcy levels were about 10.2 mmol/l, levels in the other groups were found to be:
* More than 50% higher in the vegan group (15.8 mmol/l)
* About 30% higher in the vegetarian group (13.2 mmol/l)
Serum folate levels were within the normal range for all three groups, although they were significantly lower in omnivores. The authors conclude that "The results show that the mild hyperhomocysteinemia in alternative nutrition is a consequence of vitamin B12 deficiency."
