(02-07-10) UK Food Standards Agency Workshop Report: an investigation of the relative contributions of diet and sunlight to vitamin D status.

Ashwell M, Stone EM, Stolte H, Cashman KD, Macdonald H, Lanham-New S, Hiom S,
Webb A, Fraser D.

Ashwell Associates Limited, Ashwell Street, Ashwell, Hertfordshire SG7 5PZ,
UK.
Abstract
The UK Food Standards Agency (FSA) convened an international group of
scientific experts to review three Agency-funded projects commissioned to
provide evidence for the relative contributions of two sources, dietary vitamin
D intake and skin exposure to UVB rays from sunlight, to vitamin D status. This
review and other emerging evidence are intended to inform any future risk
assessment undertaken by the Scientific Advisory Committee on Nutrition.
Evidence was presented from randomised controlled trials to quantify the amount
of vitamin D required to maintain a serum 25-hydroxy vitamin D (25OHD)
concentration >25 nmol/l, a threshold that is regarded internationally as
defining the risk of rickets and osteomalacia. Longitudinal evidence was also
provided on summer sunlight exposure required to maintain 25OHD levels above
this threshold in people living in the British Isles (latitude 51 degrees -57
degrees N). Data obtained from multi-level modelling of these longitudinal
datasets showed that UVB exposure (i.e. season) was the major contributor to
changes in 25OHD levels; this was a consistent finding in two Caucasian groups
in the north and south of the UK, but was less apparent in the one group of
British women of South Asian origin living in the south of the UK. The FSA-
funded research suggested that the typical daily intake of vitamin D from food
contributed less than UVB exposure to average year-round 25OHD levels in both
Caucasian and Asian women. The low vitamin D status of Asian women has been
acknowledged for some time, but the limited seasonal variation in Asian women
is a novel finding. The Workshop also considered the dilemma of balancing the
risks of vitamin D deficiency (from lack of skin exposure to sunlight in
summer) and skin cancer (from excessive exposure to sunlight with concomitant
sunburn and erythema). Cancer Research UK advises that individuals should stay
below their personal sunburn threshold to minimise their skin cancer risk. The
evidence suggests that vitamin D can be produced in summer at the latitude of
the UK, with minimal risk of erythema and cell damage, by exposing the skin to
sunlight for a short period at midday, when the intensity of UVB is at its
daily peak. The implications of the new data were discussed in the context of
dietary reference values for vitamin D for the general population aged 4-64
years. Future research suggestions included further analysis of the three FSA-
funded studies as well as new research.

Source: Br J Nutr. 2010 Jun 4:1-9. [Epub ahead of print]

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