Vitamin D status and glucose homeostasis in the 1958 British birth cohort: the role of obesity.
OBJECTIVE
Obesity is a well-known risk factor for vitamin D deficiency. We evaluated the interrelationship between vitamin D status, body size, and glucose homeostasis, measured by HbA1c (A1C).


METHODS
Data are from the survey of the 45-year-old 1958 British birth cohort (2002-2004). Information on A1C, 25-hydroxyvitamin D [25(OH)D; an indicator of vitamin D status], and BMI was collected from 7,198 Caucasian subjects.


RESULTS
25(OH)D was < 75 nmol/l in 80% of the obese subjects (BMI > or = 30 kg/m2) versus 68% of the other subjects (P < 0.0001). Serum 25(OH)D decreased and A1C increased by increasing BMI (P < 0.0001 for both comparisons). There was a nonlinear association between 25(OH)D and A1C: a steep linear decrease in A1C by 25(OH)D until 65 nmol/l and only smaller decreases with further increases. There was evidence for effect modification by BMI in the association between 25(OH)D and A1C (P < 0.0001), and differences appeared stronger for participants with higher compared with lower BMIs. After adjustment for sex, season, geographical location, physical activity, and social class, percent change in A1C by 10-nmol/l increase in 25(OH)D was -0.21 (95% CI -0.31 to -0.11) for BMI < 25 kg/m2, -0.25 (-0.37 to -0.13) for BMI 25-29.9 kg/m2, -0.65 (-0.95 to -0.34) for BMI 30-34.9 kg/m2, and -1.37 (-2.09 to -0.64) for BMI > or = 35 kg/m2.


CONCLUSIONS
Body size was a strong determinant for 25(OH)D, with concentrations being suboptimal in most obese participants. Randomized controlled trials [using dosages sufficient to improve 25(OH)D also for the obese] are required to determine whether clinically relevant improvements in glucose metabolism can be obtained by vitamin D supplementation.
Hyppönen
Elina
E
Centre for Paediatric Epidemiology and Biostatistics, Institute of Child Health, 30 Guildford St., London, WC1N 1EH, UK. e.hypponen@ich.ucl.ac.uk
Power
Chris
C
D001786:Blood Glucose / Q000378:metabolism*; D015992:Body Mass Index; D006442:Glycated Hemoglobin / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism
D001786:Blood Glucose; D006442:Glycated Hemoglobin; D014807:Vitamin D; C104450:25-hydroxyvitamin D