A study published in the Annals of Neurology by a team of researchers from the Houston Methodist Neurological Institute and Erasmus Medical Center finds that women who are not able to make enough thyroid hormone are four times more likely to give birth to autistic children. The paper took data from 4,000 Dutch mothers and their children and supports previous work that asserts a lack of maternal thyroid hormone affects the movement of fetal brain cells during embryonic development. This means that autism could be in large part due to environmental factors instead of genetics, and that prevention is possible.
The paper also notes that women who do not produce enough T4, also known as thyroxin, can have children with more pronounced autistic symptoms. Dutch mothers in the study had their blood drawn at the thirteenth week of their pregnancy to measure for thyroxin and two proteins that indicate low levels of the hormone. From a sample of 4,039, the team identified 80 children who showed signs of autism and 159 mothers were classified as being extremely T4 deficient. The researchers found a weak association between mild T4 deficiencies, but a strong correlation between severe deficiencies and autism.
Thyroid hormone deficiencies are largely due to a lack of dietary iodine, a condition that is common around the world. According to the World Health Organization, one in three people need more iodine to ensure thyroid health. Thanks to programs in the United States, only one in seven people lack sufficient levels of iodine. Luckily, supplements like iodized salt can go a long way towards the prevention of the disorder.