Health & beauty
Vitamin D deficiency
Introduction
Many children and adults aren't getting enough vitamin D. This could have serious health consequences.
Vitamin D deficiency, particularly in children, is a growing problem worldwide. We look at possible reasons why, and how to boost your levels.
What is vitamin D?
Vitamin D helps the body to absorb calcium and phosphorus, which are essential for bone development. As well, it's important for muscle development, as impaired muscle function can lead to accidents and falls, particularly in older people. A year-long study of 1231 adults aged 65 years or older found that those deficient in vitamin D were 78 percent more likely than people with adequate levels to have at least two falls.
Other studies are finding that it may have wider health benefits such as helping prevent cancers of the breast, colon, and prostate. It may also help reduce the risk of diabetes, hypertension, and multiple sclerosis, and slow the progression of osteoarthritis.
Over 90 percent of our daily vitamin D requirement is provided by the action of sunlight on the skin: UV (ultra-violet) radiation penetrates the skin and activates a precursor of vitamin D. Some foods contain vitamin D - the main sources are oily fish (like salmon and sardines), liver, eggs, and cheese.
Yoghurt, skim and reduced fat milks, dairy desserts, butter and margarines, and food drinks are allowed to be fortified with vitamin D. But you're unlikely to get enough vitamin D through diet alone.
What's the problem?
Vitamin D deficiency, particularly in children, is a growing problem worldwide.
The most serious consequence of this deficiency in children is rickets, a nutritional disorder that leads to bone deformities such as bowed legs.
In New Zealand, the 2002 National Children's Nutrition Survey of 5-to-14-year-olds found that:
- 4 percent of children surveyed were vitamin D-deficient
- nearly 33 percent of them had vitamin D levels low enough to affect bone density.
As well, two surveys have found that almost half the population is likely to have insufficient vitamin D.
Who's missing out?
People with dark or olive skin are at greater risk of vitamin D deficiency than those with light skin. Melanin, the pigment in skin, acts as a natural sunscreen - so people with darker skin need greater exposure to sunlight, to synthesise similar amounts of vitamin D. The National Children's Nutrition Survey found that 60 percent of Pacific children were vitamin D-deficient, compared with 32 percent of all children in the survey.
Others at risk are people in communities where the skin must be covered up for cultural or religious reasons, the elderly (if they are house-bound), and breast-fed babies of vitamin D-deficient mothers.
As well, our lifestyle and work environment could be contributing to vitamin D deficiency. In summer, a few minutes' sun exposure most days in mid morning or early afternoon to the face, arms and hands or legs is enough to maintain vitamin D levels.
But in winter, when UV levels are low and days are shorter, it's tempting to stay inside in front of the TV or computer. Many people leave for work early in the morning, drive to work, eat lunch inside, and drive home - for 5 days a week. Some wear sun-protective skin creams all year round to protect against UV-ageing of their skin.
Our advice
- The best way to boost your vitamin D is to get out and about during the winter - go for a walk at lunchtime when UV levels are highest. But always wear a sunscreen when skiing - UV levels are much higher at high altitudes.
- Talk to a health professional before taking a vitamin D supplement. Although it is difficult to actually get too much vitamin D, it is harmful in very high doses - the side effects range from nausea and weakness to kidney and heart failure.
- Don't use the health benefits of vitamin D as an excuse for getting a tan in summer - skin cancer is a major health hazard. Vitamin D is made most efficiently by brief, frequent sun exposures. It is broken down by too much sun.