People with very pale skin may be unable to spend enough time in the sun to make the amount of vitamin D the body needs - while also avoiding sunburn. Such people may need vitamin D supplements, suggest researchers at the University of Leeds, funded by Cancer Research UK.
The study, published in Cancer Causes and Control
*, suggested that melanoma patients may need vitamin D supplements as well.
But researchers also noted that sunlight and supplements are not the only factors that can determine the level of vitamin D in a person's body.
Some inherited differences in the way people's bodies process vitamin D into the active form also have a strong effect on people's vitamin D levels.
The study defined the optimal amount of vitamin D required by the body as at least 60nmol/L. However at present there is no universally agreed standard definition of an optimal level of vitamin D.
Professor Julia Newton-Bishop, lead author of the study based in the Cancer Research UK Centre at the University of Leeds, said: "Fair-skinned individuals who burn easily are not able to make enough vitamin D from sunlight and so may need to take vitamin D supplements.
"This should be considered for fair-skinned people living in a mild climate like the UK and melanoma patients in particular."
Researchers took the vitamin D levels of around 1,200 people and found that around 730 people had a sub-optimal level. Those with fair-skin had significantly lower levels.Researchers chose 60nmol/L as the optimal vitamin D level in part because there is evidence that levels lower than this may be linked to greater risk of heart disease and poorer survival from breast cancer.
A consensus between health charities including Cancer Research UK says that levels below 25nmol/L are vitamin D deficient which means that these levels are associated with poor bone health. But some researchers consider that higher levels, around 60nmol/l, may be desirable for optimal health effects.
Sara Hiom, director of health information at Cancer Research UK, said: "We must be careful about raising the definition of deficiency or sufficiency to higher levels until we have more results from trials showing that maintaining such levels has clear health benefits and no health risks.
"If you are worried about your vitamin D levels, our advice is to go see your doctor."