Vitamin D exposed to limelight

RECENT science had given us the knowledge that vitamin D is responsible for the absorption of calcium and phosphate in the intestines. We also now know that, in humans at least, this vitamin is unique in that it can either be ingested as vitamin D3 or D2 or, otherwise, form (synthesise) from cholesterol when the body is exposed to enough sunlight.

More recently, vitamin D has been hurled back into the science headlines with the publication of two important studies, one linking the vitamin to autism prevention and treatment, and the other to cognitive health.

Role in reducing the risk of autism

The American study published in the peer-reviewed online journal Dermato-Endocrinology claims to have found additional evidence that vitamin D reduces the risk of developing autism. This, after it examined a variation of autism prevalence by state for subjects aged 6-17 years in 2010. The study found that U.S. states with higher solar ultraviolet-B (UVB) doses in summer or autumn had half the rate of autism.In states with the least solar UVB, black Americans had a 40% higher rate of autism than white Americans, according to the study. Black Americans have lower vitamin D or serum 25-hydroxyvitamin D [25(OH)D] concentrations due to their darker skin, compounded by the fact that solar UVB is the primary source of vitamin D for most Americans.

Similar geographical variations regarding the incidence and mortality rates of about 15 types of cancer in the United States have also been noted. The UVB–vitamin D–cancer hypothesis was first proposed in 1980, based on variations in the mortality rates of colon cancer in the United States.The hypothesis now has strong support from observational studies and laboratory studies of mechanisms, and limited support from randomised controlled trials. In all of these, subjects with lower serum 25(OH) D concentrations were found to have a greater risk of developing breast and colorectal cancer. Additionally, those with lower 25(OH)D concentrations at the time they were diagnosed of cancer were found to have a much lower survival rate for seven types of cancer.

Medical studies that corroborate one another emphasise the function of vitamin D in cognitive health. The lack of this vitamin in the diet may be one of the causes of dementia – even Alzheimer’s disease –in the elderly
Photo ? Jonathan Ross I Dreamstime.com

In the mid-1930s, similar geographical variations had been reported in dental caries amongst white boys aged 12-14 years; these were also linked to the amount of sunshine. The dental rank of men entering the Armed Forces for both World War I and World War II also showed a similar variation with regards to their solar UVB exposure. Vitamin D reduces the risk of dental caries through the induction of cathelicidin, a substance with antibacterial effects.

These studies of geographical variation concerning diseases and how they relate to solar UVB doses are important for identifying a potential role for vitamin D in the prevention of any disease. No factor other than vitamin D has been suggested to explain the inverse correlations between solar UVB and cancer or between solar UVB and dental caries. Thus, researchers suspect that the same conclusion could be reached by ongoing and planned studies on autism.

This expectation regarding autism is now necessarily leading researchers to the question of whether maternal vitamin D deficiency during pregnancy or vitamin D deficiency in early life is related to the development of autism.

Regarding maternal vitamin D deficiency, other studies have found adverse effects on foetal brain development during the third trimester of pregnancy. These include increased risk of schizophrenia and languagShop Women's Sneakers by Brand