title: Does an active sun exposure habit lower the risk of venous thrombotic events? A D-lightful hypothesis.
abstract: BACKGROUND
  Venous and arterial thrombotic complications exhibit a seasonal variation, with risk peaking in winter and dropping to a nadir in summer. We sought a possible correlation between sun exposure habits and venous thromboembolism (VTE) events.
  
  
  METHODS
  This was a cohort study comprising 40,000 women (1000 per year of age from 25 to 64 years) who were drawn from the southern Swedish population registry for 1990 and followed for a mean of 11 years. Seventy-four per cent answered an inquiry at the inception of the study (n=29,518), and provided detailed information on their sun exposure habits. Cox regression analysis was used with the presence of VTE as a dependent variable and selected demographics as independent variables. The main outcome was the relationship between VTE and sun exposure habits.
  
  
  RESULTS
  Swedish women who sunbathed during the summer, on winter vacations, or when abroad, or used a tanning bed, were at 30% lower risk of VTE than those who did not. Risk estimates did not change substantially after adjustment for demographic variables. The risk of VTE increased by 50% in winter as compared to the other seasons; the lowest risk was found in the summer.
  
  
  CONCLUSIONS
  Women with more active sun exposure habits were at a significantly lower risk of VTE. We speculate that greater ultraviolet B light exposure improves a person's vitamin D status, which in turn enhances anticoagulant properties and enhances the cytokine profile.
authors.affiliation: Department of Obstetrics and Gynecology, Clintec, Karolinska University Hospital, Huddinge, Stockholm, Sweden. pelle.lindqvist@ki.se
authors.forename: P G
authors.initials: PG
authors.lastname: Lindqvist
authors.forename: E
authors.initials: E
authors.lastname: Epstein
authors.forename: H
authors.initials: H
authors.lastname: Olsson