title: Reproductive history, lifestyle factors and season as determinants for serum calcium concentrations in women.
abstract: OBJECTIVE
  Serum calcium concentrations have been associated with the risk of malignant disease, especially breast cancer. Thus, determinants of serum calcium concentrations, with special regard to risk factors of breast cancer, are of great interest.
  
  
  METHODS
  Previous studies have either been small or they have not focused on reproductive factors. The present study examined serum calcium concentrations in relation to reproductive history, selected lifestyle factors and screening season in a large population-based cohort study comprising 8,114 women. ANOVA followed by the Bonferroni t-test were used for comparison of means, and logistic regression and multiple regression analysis were used to test associations.
  
  
  RESULTS
  Serum calcium concentrations were lower in hormone replacement therapy users versus non-users (2.321 mmol/L versus 2.364; p<0.001) and in users of oral contraceptives versus non-users (2.304 versus 2.348; p<0.001). They were higher in peri-/postmenopausal versus premenopausal women (2.357 versus 2.319; p<0.001). Overweight and obese women had higher mean calcium concentrations (2.350 and 2.355) than women with body mass index between 20 and 25 (2.342; p<0.001). Serum calcium concentrations were higher in spring and autumn than in winter (2.352 and 2.353 versus 2.343; p = 0.002). Both younger (40-45 years) (2.334; p = 0.001) and older age groups (>55 years) (2.363; p<0.001) had higher mean calcium concentrations compared to those of women aged 45-50 years (2.320), even when adjusting for menopausal status, suggesting that age has an independent influence on calcium concentrations.
  
  
  CONCLUSIONS
  It is concluded that reproductive factors such as menopausal status, use of oral contraceptives or hormone-replacement therapy, and age, BMI and season are associated with serum calcium concentrations.
authors.affiliation: Department of Surgery, Malmö University Hospital, Malmö, Sweden. martin.almquist@med.lu.se
authors.forename: Martin
authors.initials: M
authors.lastname: Almquist
authors.forename: Anne-Greth
authors.initials: AG
authors.lastname: Bondeson
authors.forename: Lennart
authors.initials: L
authors.lastname: Bondeson
authors.forename: Cat
authors.initials: C
authors.lastname: Halthur
authors.forename: Johan
authors.initials: J
authors.lastname: Malm
authors.forename: Jonas
authors.initials: J
authors.lastname: Manjer
mesh_terms: D017677:Age Distribution; D002118:Calcium / Q000097:blood*; D005260:Female; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D016017:Odds Ratio; D012044:Regression Analysis; D017584:Reproductive History; D012621:Seasons
chemical_list: D002118:Calcium