Most of us know that calcium is essential for healthy bones, but not many are aware that vitamin D is equally essential for absorption of calcium and the growth of strong bones.

Experts are unanimous that a person should spend 10 to 15 minutes under the sun every day to get the essential vitamin.

A survey by the University of Hong Kong (HKU) has found 30 per cent of Hong Kong's post-menopausal women had not heard of vitamin D. And more than 40 per cent of the 540 women (aged 50 and above), covered by the survey were not aware that it was necessary for healthy bones.

Annie Kung, of HKU's faculty of medicine, said: "Vitamin D inadequacy is a factor that causes osteoporosis." Osteoporosis, or the decrease in bone mass and density, affects mainly women after menopause and a smaller number of men. Osteoporosis makes the bones more prone to fracture, can cause severe disability and can have a fatality rate of as high as 20 per cent.

About 290,000 women and 100,000 men are suffering from the disease in Hong Kong today, and figures suggest that by 2031, 740,000 women and a quarter million men could be suffering from it. More than half of the Hong Kong's women have vitamin D deficiency.

"Calcium is a locked door and vitamin D is the key that opens the door," explained Kung. Without sufficient vitamin D, consuming any amount of calcium would be meaningless because calcium alone cannot leave the intestine to enter the bloodstream," Kung said.

"Though sufficient amounts of vitamin D (400 international units) could be easily absorbed by spending 10 to 15 minutes under the sun every day or by eating fish such as salmon and tuna, most respondents didn't know its sources. It reflected the fact that public knowledge of vitamin D is very, very low," Kung said.

Ms Yip, a retired teacher suffering from osteoporosis, said that before receiving treatment, she could not walk up slopes or kneel down properly. Since undergoing medical consultation two years ago, she could now do whatever she liked.

Kung urged people to go out in the sun for a short while every day. For those fearing that it may burn their skin, she said it would be best to put on sunscreen after 10 minutes under the sun as anything above SPF 8 would completely block ultra violet rays.

Sitting next to a window would not be enough as the glass would block such rays.

Another option is to take vitamin D supplements, according to the experts.

The recommended daily dosage for adults is 400 international units, but if one takes more than 2,000 international units, it could lead to hyper calcaemia and formation of stones in the bladder.

"If you are an inch shorter than you used to be or if you have a hunchback and your head cannot touch the wall when you stand against it, it maybe a sign of osteoporosis," Kung said, offering tips to the public.

(HK Edition 11/23/2005 page2)