Fair-skinned people who burn easily may need to take vitamin D supplements, according to research.
Researchers at Leeds University say that those who do not spend enough time in the sun may be lacking the essential vitamin that the body makes from sunlight.
The new study, funded by Cancer Research UK, have found that even with a lot of sun exposure, those with fair skin may not be able to make enough vitamin D.
NHS advice say that short daily periods of sun exposure - around 10 or 15 minutes - without sunscreen is sufficient for most people, although there is not one recommedation that suits everybody.
The researchers say that increasing direct sun exposure is not the ideal way to increase vitamin D levels as it increases the risk of skin cancer, whereas supplements could be.
"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," Professor Julia Newton-Bishop, lead author of the study based in the Cancer Research UK Centre at the University of Leeds, said.
"This should be considered for fair-skinned people living in a mild climate like the UK and melanoma patients in particular," she said.
The study examined 1,200 people. Of these, 730 were found to have "lower than optimal" vitamin D levels - and many of these were people with very pale, freckled skin.
The study, published in the journal Cancer Causes and Control, suggests the optimal amount of vitamin D required by the body is at least 60nmol/L.
Levels below 25nmol/L are linked to poor bone health.
The new study showed that people with fair skin did not, on average, reach 60nmol/L unless they were taking supplements, but did reach above 25nmol/L.
"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," said Sara Hiom, director of health information at Cancer Research UK.