title: Seasonal variation of 25-hydroxyvitamin D among non-Hispanic black and white pregnant women from three US pregnancy cohorts.
abstract: BACKGROUND
  Vitamin D deficiency during pregnancy has been associated with increased risk of complications and adverse perinatal outcomes. We evaluated seasonal variation of 25-hydroxyvitamin D [25(OH)D] among pregnant women, focusing on patterns and determinants of variation.
  
  
  METHODS
  Data came from three cohort studies in the US that included 2583 non-Hispanic Black and White women having prenatal 25(OH)D concentrations determined. Fourier time series and generalised linear models were used to estimate the magnitude of 25(OH)D seasonality. We modelled seasonal variability using a stationary cosinor model to estimate the phase shift, peak-trough difference, and annual mean of 25(OH)D.
  
  
  RESULTS
  We observed a peak for 25(OH)D in summer, a nadir in winter, and a phase of 8 months, which resulted from fluctuations in 25(OH)D3 rather than 25(OH)D2. After adjustment for covariates, the annual mean concentrations and estimated peak-trough difference of 25(OH)D among Black women were 19.8 ng/mL [95% confidence interval (CI) 18.9, 20.5] and 5.8 ng/mL [95% CI 4.7, 6.7], and for non-Hispanic White women were 33.0 ng/mL [95% CI 32.6, 33.4] and 7.4 ng/mL [95% CI 6.0, 8.9].
  
  
  CONCLUSIONS
  Non-Hispanic Black women had lower average 25(OH)D concentrations throughout the year and smaller seasonal variation levels than non-Hispanic White women. This study's confirmation of 25(OH)D seasonality over a calendar year has the potential to enhance public health interventions targeted to improve maternal and perinatal outcomes.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Luque-Fernandez
authors.forename: Bizu
authors.initials: B
authors.lastname: Gelaye
authors.forename: Tyler
authors.initials: T
authors.lastname: VanderWeele
authors.forename: Cynthia
authors.initials: C
authors.lastname: Ferre
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Siega-Riz
authors.forename: Claudia
authors.initials: C
authors.lastname: Holzman
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Enquobahrie
authors.forename: Nancy
authors.initials: N
authors.lastname: Dole
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Williams
mesh_terms: D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data*; D015331:Cohort Studies; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D039382:Maternal Nutritional Physiological Phenomena; D011247:Pregnancy; D037841:Pregnant People; D015995:Prevalence; D012307:Risk Factors; D012621:Seasons; D013472:Sunlight; D014481:United States / Q000453:epidemiology; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000627:therapeutic use; D014808:Vitamin D Deficiency / Q000150:complications* / Q000178:diet therapy / Q000453:epidemiology*; D044465:White People / Q000706:statistics & numerical data*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: 25-hydroxyvitamin D; epidemiology; pregnant women; season; vitamin D