Abstract
In prospective observational cohort studies, increasing sun exposure habits have been associated with reduced risk of cardiovascular mortality. Our aim was to assess possible observational mechanisms for this phenomenon. A written questionnaire was answered by 23,593 women in the year 2000 regarding risk factors for melanoma, including factors of possible interest for hypertension, such as detailed sun exposure habits, hypertension, marital status, education, smoking, alcohol consumption, BMI, exercise, and chronic high stress. Hypertension was measured by the proxy “use of hypertension medication” 2005–2007, and high stress by “need of anti-depressive medication”. Sun exposure habits was assessed by the number of `yes’ to the following questions; Do you sunbath during summer?, During winter vacation?, Do you travel south to sunbath?, Or do you use sun bed? Women answering ‘yes’ on one or two questions had moderate and those answering ‘yes’ on three or four as having greatest sun exposure. The main outcome was the risk of hypertension by sun exposure habits adjusted for confounding. As compared to those women with the greatest sun exposure, women with low and moderate sun exposure were at 41% and 15% higher odds of hypertension (OR 1.41, 95% CI 1.3‒1.6, p < 0.001 and OR 1.15, 95% CI 1.1‒1.2, p < 0.001), respectively. There was a strong age-related increased risk of hypertension. Other risk factors for hypertension were lack of exercise (OR 1.36), a non-fair phenotype (OR 1.08), chronic high stress level (OR 1.8), and lack of university education (OR 1.3). We conclude that in our observational design sun exposure was associated with a dose-dependent reduced risk of hypertension, which might partly explain the fewer deaths of cardiovascular disease with increasing sun exposure.
Highlights
An inverse association has been shown between cardiovascular disease (CVD) and vitamin D levels [1,2,3]
In this study we find an inverse dose-dependent association between sun exposure habits and hypertension, adjusted for possible covariates
We sought to assess if the lower CVD mortality associated with active sun exposure habits might be mediated through a persistent reduction in blood pressure, which was found
Summary
An inverse association has been shown between cardiovascular disease (CVD) and vitamin D levels [1,2,3]. It has been reported that at high latitudes women with active sun exposure habits have been associated with greater life expectancy, compared to those with inactive sun habits [7,8,9]. Compared to those with moderate and greatest sun exposure habits, women > 55 years of age with low sun exposure habits were at 1.5-fold and 2.3-fold, increased likelihood of death from CVD and one month shorter life expectancy per year [9, 10]. In terms of CVD mortality, low vitamin D levels may be a marker of low sun exposure. Those with active sun exposure habits have sufficient vitamin D levels all year around, while those with inactive sun exposure are at low levels most of the year [11]
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