Researchers at Duke-NUS Medical School have found that low vitamin D levels signal cognitive impairment in elderly Chinese people.
Professor David Matchar, director of the Health Services and Systems Research Programme at Duke-NUS, led a team of six others in a two-year study of 1,202 subjects with a mean age of 80 from eight different provinces in China.
They split the participants into four groups of varying vitamin D3 levels measured at the start of the study. Vitamin D3 is the most common form of vitamin D circulating in the bloodstream. The participants were chosen based on age and had no signs of cognitive impairment.
For two years, they were tested on their level of cognitive function using the Mandarin version of a "mini-mental status examination", which allocated up to 30 points to each person based on performance.
A decrease of three or more points suggested a decline in cognitive function, and falling below the threshold of 18 at the end of two years indicated cognitive impairment.
Some facts about 'sunshine vitamin
Vitamin D, sometimes called the ''sunshine vitamin'' because it is produced in the body with mild sun exposure, is essential for strong bones and teeth. Here are more features about the vitamin:
*Its deficiency results in increased risk of cardiovascular diseases and neurodegenerative diseases such as Alzheimer's.
*Supplements can be taken to maintain healthy levels, with the recommended amount being 600 international units (IU) a day, and 800IU daily for those
over 70 years old.
*To get vitamin D from sunlight, the best time to do so is at midday,when the sun is overhead, as there is maximum UVB
light which promotes the vitamin's formation.
*The length of sunning time varies. Those with a lighter skin tone need about 15 minutes a day, while those with darker skin tones may need one hour or more. Out in the sun, the body knows when it has enough and will stop vitamin D formation.
*Staying by a window indoors will not help as glass filters out UVB rays.
*Vitamin D is fat-soluble and any excess will be stored in the body. In contrast, excess water-soluble vitamins can be excreted through the urine. An overdose of vitamin D from supplements could result in constipation, nausea and kidney stones.
Goh Yan Han
Prof Matchar's team found that the group with the lowest levels of vitamin D3 was three times more likely to develop cognitive impairment than the group with the highest levels of vitamin D3.
The mean level of vitamin D3 in the lowest group was 25.1 nanomoles per litre (nmol/L), while the mean for the highest group was 66.4nmol/L. Normal levels of vitamin D3 would be between 50 and 70nmol/L, said Prof Matchar.
It was the first large-scale longitudinal study on an Asian population with regard to vitamin D levels and cognitive impairment.
Previous studies on populations in Europe and North America showed similar results, said Prof Matchar.
He said: "Although this study was conducted on subjects from China, the results are applicable to regions in Asia where a large proportion of the elderly are ethnically Chinese, like Singapore."
The study is especially relevant to Singapore, he said, with its rapidly ageing population and an estimated 40,000 people with cognitive impairments here. He expects the figure to hit 80,000 within a decade.
Common causes of cognitive impairment here include Alzheimer's disease and vascular dementia. The study shows low vitamin D levels increase the risk of such diseases.
Prof Matchar recommends monitoring one's vitamin D levels and taking daily supplements or spending time in the sun when it is overhead, providing maximum ultraviolet B light, which promotes the vitamin's formation in the body.