The study, published in Cancer Causes and Control, suggested that people with very pale skin, in addition to skin cancer patients, may require supplements to boost levels of the sunshine vitamin.
“Sun exposure was associated with increased vitamin D levels, but levels more than 60 nmol/L were reached on average only in individuals reporting lengthy exposure,” explained the researchers, led by Professor Julia Newton-Bishop, from the Cancer Research UK Centre at the University of Leeds, UK.
“Sun-sensitive individuals did not achieve optimal levels without supplementation, which therefore should be considered for the majority of populations living in a temperate climate and melanoma patients in particular,” they added.
However, the researchers added that sunlight and supplements are not the only factors that determine vitamin D levels, noting that certain inherited differences in the way people's bodies process vitamin D into the active form also have a strong effect.
The sunshine vitamin
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.
The science supporting the muscle function of vitamin D, as well as the vitamin’s role in immune health, is sufficiently robust to have merited a positive opinion from the European Food Safety Authority’s (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA). Despite such proclamations of support, many people across the world are not getting enough vitamin D.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
The researchers examined the sun exposure, supplementation status, and vitamin D levels of around 1,200 participants, finding that around 730 people had a sub-optimal level – The study defined optimal levels of vitamin D as at least 60nmol/L.
Newton-Bishop and her colleagues explained that they 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.”
The researchers found that after adjustment for potential confounders including season, age, sex, and body mass index, sub-optimal vitamin D levels were significantly more frequent in sun-sensitive individuals such as people with fair-skin.
“Vitamin D levels of 60 nmol/L in the non-sun-sensitive individuals were achieved after an average 6 h/day summer weekend sun exposure but not in the sun-sensitive individuals. Users of supplements had levels on average 11.0 nmol/L higher,p = <0.0001, and achieved optimal levels irrespective of sun exposure,” said Newton-Bishop and her team
However, the UK’s NHS Choices service explained that “it is too soon to recommend supplements for fair skinned individuals and more research is needed.”
“Though the study shows some associations between some factors and vitamin D, its design cannot prove causation,” it said.
Sara Hiom, director of health information at Cancer Research UK added: "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.”
Source: Cancer Causes and Control
Published online ahead of print, doi: 10.1007/s10552-011-9827-3
“The determinants of serum vitamin D levels in participants in a melanoma case–control study living in a temperate climate”
Authors: J.R. Davies, Y-M. Chang, H. Snowden, M. Chan, S. Leake, B. Karpavicius, et al