A study by Cornell University reported autism cases within certain counties in California and Pennsylvania rose at rates that closely matched cable subscriptions, rising fastest in counties with the fastest-growing cable rates. At the same time, autism and rainfall patterns in California, Pennsylvania and Washington State also correlated with rising autism rates.
The researchers concluded that approximately 17% of the growth in autism in California and Pennsylvania during the 1970s and 1980s was due to the growth of cable television, and just under 40% of autism diagnoses in the three states studied is the result of television watching due to precipitation.
Although the rainfall portion of the study was intended to imply that children spend more time inside watching television on rainy days, the correlation between television and autism may actually be due to vitamin D deficiency. If children are spending less time in the sun, their vitamin D levels will drop accordingly.
The increased prevalence of autism over the last 20 years corresponds with escalating medical advice to avoid the sun. Researchers have determined that an insufficient intake of vitamin D lowers the vitamin D (calcitriol) levels in developing brains.
Scientists have also found that autism is more common in areas of impaired UVB penetration such as pole-ward latitudes, urban areas, areas with high air pollution, and areas of high precipitation. In addition, autism is more common in dark-skinned persons and maternal vitamin D deficiency is extremely common in those with dark-skinned. Based on these facts, experts now recommend that people with autism be checked for vitamin D deficiency.