Objective: Evidence from randomised controlled trials
suggests that vitamin D may reduce multimorbidity,
but very few studies have investigated specific
determinants of vitamin D2 and D3 (two isoforms of
25-hydroxyvitamin D). The aim of the study was to
investigate the determinants of vitamin D2 and D3 and
to identify the risk factors associated with
hypovitaminosis D.
Design: Cross-sectional study.
Setting: Northern Finland Birth Cohort 1966.
Participants: 2374 male and 2384 female participants
with data on serum 25(OH)D2 and 25(OH)D3
concentrations measured at 31 years of age (1997),
together with comprehensive measures of daylight,
anthropometric, social, lifestyle and contraceptive
cofactors.
Methods: We assessed a wide range of potential
determinants prior to a nationwide fortification
programme introduced in Finland. The determinants of
25(OH)D2, 25(OH)D3 and 25(OH)D concentrations were
analysed by linear regression and risk factors for being
in lower tertile of 25(OH)D concentration by ordinal
logistic regression.
Results: At the time of sampling, 72% of the
participants were vitamin D sufficient (≥50 nmol/L).
Low sunlight exposure period (vs high) was associated
positively with 25(OH)D2 and negatively with 25(OH)D3
concentrations. Use of oral contraceptives (vs nonusers)
was associated with an increase of 0.17 nmol/L
(95% CI 0.08 to 0.27) and 0.48 nmol/L (95% CI 0.41
to 0.56) in 25(OH)D2 and 25(OH)D3 concentrations.
Sex, season, latitude, alcohol consumption and
physical activity were the factors most strongly
associated with 25(OH)D concentration. Risk factors
for low vitamin D status were low sunlight exposure
defined by time of sampling, residing in northern
latitudes, obesity, higher waist circumference, low
physical activity and unhealthy diet.
Conclusions: We demonstrate some differential
associations of environmental and lifestyle factors with
25(OH)D2 and 25(OH)D3 raising important questions
related to personalised healthcare. Future strategies
could implement lifestyle modification and supplementation to improve vitamin D2 and D3 status,
accounting for seasonal, lifestyle, metabolic and
endocrine status.