title: Seasonality and ambient temperature at time of conception in term-born individuals - influences on cardiovascular disease and obesity in adult life.
abstract: BACKGROUND
  The influence of environmental conditions early in life - including temperature and season - on health later in life has so far not attracted much attention.
  
  
  OBJECTIVE
  Using data from the Helsinki Birth Cohort Study of 13,345 men and women, the influence of temperature and season at month of conception on birth weight, and on cardiovascular diseases and obesity-related traits in later life was studied.
  
  
  METHODS
  Linear regressions were fitted to examine the relationship between birth weight/obesity-related variables/hypertension and alternatively month of conception and average temperature of month of conception. The incidence of both coronary heart disease and cerebrovascular disease was assumed to follow a Weibull hazard model, and was modelled accordingly using survival analysis techniques.
  
  
  RESULTS
  In women, unusually cold temperatures at month of conception predicted lower body mass index (BMI) and fat percentage, and protected from obesity. Warmer temperatures at month of conception were associated with higher risk for hypertension. In men, warmer temperatures around conception predicted lower BMI. No seasonal influences were detected on obesity-related variables, nor were there seasonal or temperature mediated influences on birth weight, coronary heart disease or cerebrovascular disease observed.
  
  
  CONCLUSIONS
  We suggest that ambient temperature has an influence on obesity-related outcomes and hypertension. This merits further study, also with regard to other health outcomes and from a global perspective.
authors.affiliation: Department of Health Promotion and Chronic Disease Prevention, National Institute for Health and Welfare, Helsinki, Finland ; Folkhälsan Research Centre, Helsinki, Finland.
authors.forename: Nadja
authors.initials: N
authors.lastname: Schreier
authors.forename: Elena
authors.initials: E
authors.lastname: Moltchanova
authors.forename: Tom
authors.initials: T
authors.lastname: Forsén
authors.forename: Eero
authors.initials: E
authors.lastname: Kajantie
authors.forename: Johan G
authors.initials: JG
authors.lastname: Eriksson
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001719:Birth Certificates; D001724:Birth Weight; D002318:Cardiovascular Diseases / Q000209:etiology*; D003080:Cold Temperature; D005260:Female; D005306:Fertilization; D005387:Finland; D006358:Hot Temperature; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D009765:Obesity / Q000209:etiology*; D011247:Pregnancy; D016016:Proportional Hazards Models; D012042:Registries; D012307:Risk Factors; D017678:Sex Distribution; D047929:Term Birth; D013995:Time
keywords: cardiovascular disease; hypertension; obesity; seasonality; temperature