Majority of UK population fails to gain optimum vitamin D level from sunlight
MedWire News: Results from a UK study show that the majority of the White UK population do not achieve a high enough vitamin D level through exposure to sunlight over the summer to retain sufficiency throughout the winter.
Ann Webb (University of Manchester) and team recruited 125 White individuals aged 20-60 years resident in the Greater Manchester area to take part in the study. The researchers measured the participants' monthly circulating 25-hydroxyvitamin D (vitamin D) levels over 12 months.
Recent research suggests that a circulating level of vitamin D below the optimum of 32 ng/ml is associated with increased risk for conditions such as hypertension, diabetes, and multiple sclerosis.
Webb and colleagues report that from June to October, 75% of the volunteers had at least sufficient (above 20 ng/ml) vitamin D. This figure dropped to 40% in January, increasing to 55% in April.
For April and July, mean daily exposure to sunlight between 11:00 and 13:00 was 9 min during the week and 18 min at weekends. When the time period was extended to 10:00-15:00 the corresponding exposure times were 22 and 49 min.
The highest mean levels of vitamin D were recorded in September, at 28.4 ng/ml, when 28% of the group had optimal and 0% deficient (below 5 ng/ml) status. Lowest mean levels occurred in February, at 18.3 ng/ml, when only 7% of the group had optimal and 5% had deficient status.
"Thus, while UK summer sun exposure protects the White, adult population from clinical vitamin D deficiency, less than one-third of the population (28% in September) reaches the proposed optimal vitamin D levels even in summer," say the researchers.
They found that in order to retain vitamin D sufficiency in February, mean late summer levels of 30.4 and 34.9 ng/ml in women and men, respectively, were required.
"We suggest the proposed optimal vitamin D status might be better considered as an end of summer rather than a year-round goal," conclude the authors in the British Journal of Dermatology.
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By Helen Albert