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The determinants of serum vitamin D levels in participants in a melanoma case-control study living in a temperate climate.

ABSTRACT:

Background

We report the determinants of serum levels of vitamin D in a U.K. melanoma case-control study benefitting from detailed exposure and genotyping data.

Methods

Sun exposure, supplemental vitamin D, and SNPs reported to be associated with serum levels were assessed as predictors of a single serum 25-hydroxyvitamin D3 measurement adjusted for season, age, sex, and body mass index.

Results

Adjusted analyses showed that vitamin D levels were sub-optimal especially in the sun-sensitive individuals (-2.61 nmol/L, p = 0.03) and for inheritance of a genetic variant in the GC gene coding for the vitamin D-binding protein (-5.79 for heterozygotes versus wild type, p = <0.0001). Higher levels were associated with sun exposure at the weekend in summer (+4.71 nmol/L per tertile, p = <0.0001), and on hot holidays (+4.17 nmol/L per tertile, p = <0.0001). In smoothed scatter plots, 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.

Conclusions

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 (?12 h/weekend). The 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. Inherited variation in genes such as GC is a strong factor, and carriers of variant alleles may therefore require higher levels of supplementation.

SUBMITTER: Davies JR

PROVIDER: S-EPMC3176401 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSaudi women are at risk of vitamin D deficiency because they are fully covered by traditional clothing and because of their indoor lifestyle. The latest national study reported that vitamin D deficiency (serum 25(OH)D < 50 nmol/L) affects 72% of young Saudi women. Because little information is available regarding knowledge on vitamin D, attitudes toward sun exposure, and the vitamin D status of premenopausal women in Jeddah, more research is necessary in order to develop effective intervention programs. The purpose of this study is to explore how the relationship between knowledge of vitamin D and attitudes about sun exposure affect the serum 25(OH)D levels in premenopausal Saudi women.MethodsThis cross-sectional study included 257 women aged 20-50 years attending the primary care clinic in Jeddah, Saudi Arabia. Participants completed questionnaires about socio-demographics, dietary vitamin D intake, attitudes toward sun exposure, and were tested on their knowledge of vitamin D. Serum 25(OH)D was evaluated using chemiluminescent microparticle immunoassay.ResultsAlthough 99% of participants had heard of vitamin D and 91% knew that sunlight exposure is a primary source of vitamin D, they also expressed the feeling of having insufficient knowledge regarding vitamin D sources. Furthermore, the majority of participants had negative attitudes toward sun exposure. High fish consumption was associated with a higher level of knowledge regarding vitamin D. The binary logistic regression indicated that low levels of knowledge about vitamin D were associated with low education levels (odds ratio = 0.397, 95% CI = [0.206, 0.765], p = 0.019) and with being married (odds ratio = 0.522, 95% CI = [0.281, 0.971], p = 0.04). In addition, spending time outside in the sun was significantly associated with increased serum 25(OH)D levels (p = 0.006), and the wearing of colored abaya was significantly associated with increased serum 25(OH)D levels (p = 0.008).ConclusionSuboptimal vitamin D status and insufficient knowledge of vitamin D intake sources are common in premenopausal women in Jeddah. Based on this data, health professionals could provide medical intervention to the most vulnerable female patients, as well as offer clear guidelines and information to the general public.