“There is already a wide body of scientific benefits that supports vitamin D in bone health, and now there is evidence for its wider benefits. There is still emergeing research on the effects of vitamin D on cognitive health,” Wong told NutraIngredients-USA.
Wong referred specifically to the recent study showing that low vitamin D levels in elderly patients doubled the risk of Alzheimer's disease and dementia.
The largest study of its kind, published in the online medical journal of the American Academy of Neurology, found those with low levels of vitamin D in their blood (25-50 nanomole per litre) were 53% more likely to develop dementia, while those severely deficient (less than 25 nmol/L) had a 125% increased risk, compared to those with normal levels (more than 50 nmol/L).
Meanwhile for Alzheimer’s disease, people with lower levels of the vitamin were almost 70% more likely to develop the disease while this rose to 120% for those severely deficient.
The researchers looked at blood levels of vitamin D in 1,658 people aged over 65 who did not have dementia, cardiovascular disease or a history of strokes at the beginning of the trial. After an average follow-up of 5.6 years, 171 of the participants had developed dementia and 102 Alzheimer’s disease. The samples were taken from a US population–based cardiovascular study conducted between 1992–1993 and in 1999.
“In this case the researchers looked at two different blood levels of vitamin D. They used the IOM level of 50 nm per liter of 25-hydroxyvitamin D as being sufficient, and 25 nm as being severely deficient,” Wong said.
How much is enough?
In 2010, the recommended daily intake of vitamin D was bumped up from 400 IU for an adult to 600 IU. At the time, there was controversy among the researchers over this recommendation, with many saying the levels should have been put much higher, to 1,000 IU or more, and that there should have been some adjustment for latitude, as people living in Alberta will naturally get many fewer hours of sunlight on their skin annually than will a typical Florida resident.
“There still is some controversy over what is sufficient,” Wong said. “The Endocrine Society recently proposed a health cutoff of 75 nm.
“In any case, it’s obvious that vitamin D is important in many different processes in the body. There are vitamin D receptors all over the body. Vitamin D can have an effect on a wide variety of health outcomes,” she said.
Is form important?
One issue surrounding vitamin D supplementation is the form of the vitamin supplied. Vitmain D2, ergocalciferol, is derived from fungi and other plants, and so has interest for vegetarians. But it is widely regarded as being less bioavailable than vitamin D3, cholecalciferol, which is generally manufactured by irradiating lanolin, the grease derived from sheep’s wool.
In its recent comments on FDA’S proposed changes to the labels for foods and dietary supplements, CRN asked the agency to clarify its position on the bioavailability question. CRN called on the agency to take a stance on D2 and D3 by either defining them as bioequivalent or “listing a potency conversion factor if, in fact, the agency considers one form more bioactive than the other.”
“They haven’t addressed the relative potencies of vitamin D2 versus vitamin D3. There is some evidence that shows differences in the relative biopotencies of D2 and D3,” Wong said.
In any case, it’s clear that more vitamin D, in any form, is needed in the American diet, Wong said.
“Vitamin D is a nutrient of public health conscern because it is underconsumed by Americans and deficiencies are common and that is likely to continue,” she said.