Phyto-estrogènes et aliments à base de soja chez le nourrisson et l'enfant : la prudence est de mise

Autism: transient in utero hypothyroxinemia related to maternal flavonoid ingestion during pregnancy and to other environmental antithyroid agents

The incidence and prevalence of autism have increased during the past two decades. Despite comprehensive genetic studies the cause of autism remains unknown. This review emphasizes the potential importance of environmental factors in its causation. Alterations of cortical neuronal migration and cerebellar Purkinje cells have been observed in autism. Neuronal migration, via reelin regulation, requires triiodothyronine (T3) produced by deiodination of thyroxine (T4) by fetal brain deiodinases. Experimental animal models have shown that transient intrauterine deficits of thyroid hormones (as brief as 3 days) result in permanent alterations of cerebral cortical architecture reminiscent of those observed in brains of patients with autism. I postulate that early maternal hypothyroxinemia resulting in low T3 in the fetal brain during the period of neuronal cell migration (weeks 8-12 of pregnancy) may produce morphological brain changes leading to autism. Insufficient dietary iodine intake and a number of environmental antithyroid and goitrogenic agents can affect maternal thyroid function during pregnancy. The most common causes could include inhibition of deiodinases D2 or D3 from maternal ingestion of dietary flavonoids or from antithyroid environmental contaminants. Some plant isoflavonoids have profound effects on thyroid hormones and on the hypothalamus-pituitary axis. Genistein and daidzein from soy (Glycine max) inhibit thyroperoxidase that catalyzes iodination and thyroid hormone biosynthesis. Other plants with hypothyroid effects include pearl millet (Pennisetum glaucum) and fonio millet (Digitaria exilis); thiocyanate is found in Brassicae plants including cabbage, cauliflower, kale, rutabaga, and kohlrabi, as well as in tropical plants such as cassava, lima beans, linseed, bamboo shoots, and sweet potatoes. Tobacco smoke is also a source of thiocyanate. Environmental contaminants interfere with thyroid function including 60% of all herbicides, in particular 2,4-dichlorophenoxyacetic acid (2,4-D), acetochlor, aminotriazole, amitrole, bromoxynil, pendamethalin, mancozeb, and thioureas. Other antithyroid agents include polychlorinated biphenyls (PCBs), perchlorates, mercury, and coal derivatives such as resorcinol, phthalates, and anthracenes. A leading ecological study in Texas has correlated higher rates of autism in school districts affected by large environmental releases of mercury from industrial sources. Mercury is a well known antithyroid substance causing inhibition of deiodinases and thyroid peroxidase. The current surge of autism could be related to transient maternal hypothyroxinemia resulting from dietary and/or environmental exposure to antithyroid agents. Additional multidisciplinary epidemiological studies will be required to confirm this environmental hypothesis of autism.

[Evidence-based dietetics: what has to be kept in mind for the prescription of infant formulae and follow-on formulae in 2007th?]

All infant and follow-on formulae available on the market are of high quality. Nevertheless, they are not identical. Several formulae recently launched are characterized by innovations that may have interesting functional effects in some infants. The rising number of formulae and the uncertainty on the validity of the claims presented to justify these innovations make more and more difficult the prescription of a formula that has to be individually tailored for each child. A rational prescription should only be approached on the principle of evidence-based dietetics. Infant formulae satisfy by themselves the nutritional needs of infants up to 6 months of age whereas follow-on formulae should only be used after 6 months when complementary feeding has been introduced into the diet. None of these formulae can claim any nutritional superiority, in particular over breast feeding, which is the reference mode of feeding during the first 6 months of life. The nature of the protein source is the main criteria for choosing an infant formula. In the absence of breast feeding, cow's milk protein infant and follow-on formulae represent the first choice, with the exception of infants at risk for allergy, who should be exclusively fed a hypoallergenic formula during the first 6 months of life. The main interest of soy protein infant and follow-on formulae is feeding infants in vegan families. A functional benefit has only been shown for anti regurgitation formulae as well as for formulae that have the potential to soften stools. Except for the prevention of allergic disease in at-risk families with the use of hypoallergenic infant (and not follow-on) formulae, there is no convincing evidence supporting the prescription of specific formulae in a preventive approach.