S’pore study links cognitive function to vitamin D

SINGAPORE — A recent study by researchers in Singapore has found that low levels of vitamin D are associated with greater odds of cognitive impairment in the elderly in China.

The study, undertaken in 2012 by Duke-NUS Graduate Medical School Singapore, measured the vitamin D levels and cognitive abilities of 936 men and 1,068 women, who had a combined average age of 84.9 years.

The participants were from eight different areas in China and were part of the Chinese Longitudinal Healthy Longevity Survey, which started in 1998.

Studies in the United States and Europe have suggested that low levels of vitamin D can have detrimental health consequences, including cognitive impairment, which can manifest as dementia or Alzheimer’s disease.

But little work has been done in this area on Asians and this study is the largest concerning the topic in Asia, the researchers said. They initially wanted to examine the elderly in Singapore, but there was no sample large enough.

After adjusting for various factors such as age, gender and chronic conditions, researchers found that decreased vitamin D levels — less than 31.6 nanomoles per litre of blood (nmol/L) — were associated with almost twice as much risk of cognitive impairment in participants, compared with those who had higher levels of the vitamin.

This association did not vary significantly between men and women.

Vitamin D, which can be obtained from foods such as fish and eggs as well as from sunlight, is responsible for the healthy absorption of calcium and phosphorus in the body. It also plays a protective role in the brain by reducing cellular calcium that can contribute to dementia and other illnesses related to mental function, said Professor David Matchar, who led the study.

A minimum reading of 50nmol/L is considered to be adequate. In the study of elderly in China, participants had an average vitamin D level of 43.1nmol/L.

While the relationship between vitamin D and cognitive impairment has been shown, it is still not evident that vitamin D deficiency per se is a cause of diminished cognition, said Prof Matchar, who is also director of the Program in Health Services and Systems Research at Duke-NUS.

The team is now studying if vitamin D deficiency actually causes cognitive impairment and hopes to have a manuscript for publication in a month or two.

“The point of this is that, as a population ages, they’re more likely to be vitamin D deficient and that’s associated with health-related consequences,” said Prof Matchar.

Compared with the rest of the world, Asians have lower levels of vitamin D, he added, citing previous studies.

“Possible reasons for lower vitamin D levels in Asians include the tendency to avoid sun exposure and reduced intake of vitamin-D-fortified foods such as dairy products, which are less well-tolerated by Asians,” he said. Skin melanin concentrations, cultural habits and geographical latitude differences were other reasons cited.

In Singapore, based on 2009 figures from science journal Clinical Chemistry, Chinese men and women, as well as Malay men, have adequate levels of vitamin D — more than 50nmol/L. Indian men and women, as well as Malay women, have slightly lower levels, at more than 40nmol/L.

The study also involved researchers from Peking University in Beijing, China, and the Chinese Center for Disease Control and Prevention. Its findings were published in this month’s edition of the Journal of American Geriatrics Society.