I'm turning 45 in a few weeks and, although I try and stick to a balanced diet and exercise regularly to minimise the risks of disease, I do worry about my bones. I've read a lot about calcium and various vitamin supplements, but not about vitamin D. Should I be taking a vitamin D supplement at my age?

You are worrying too much. If you are certain your diet is well-balanced and you exercise, there's nothing to worry about, especially if you are doing some outdoor sports.

The body's daily requirement for vitamin D is relatively low. It's naturally produced in the body. Exposure to sunshine for about 10 to 15 minutes at least three times a week is enough to meet your body's requirement.

The vitamin can easily be found in foods like egg, beef and liver, mushrooms, catfish, tuna, sardines and eel.

Vitamin D deficiency decreases the calcium absorption, resulting in weak bones. Such deficiencies often occur in women who don't want to brave the sunlight, urban children who lack outdoor activities, and mothers who have many children or who breastfeed for overly long periods. I've never heard of anyone getting too much vitamin D from the sun, although too much can burn the skin and may cause cancer.

Over-consumption of vitamin D can be dangerous, as it stimulates excessive calcium absorption, resulting in kidney stones.

Obtaining vitamin D naturally - through food and exposure to sunlight-should be enough for most people.

Assoc Prof Somjai Wichaidit is a nutritionist and Secretary General for Foundation for Health Sciences Promotion.