SAN DIEGO – Low levels of vitamin D are associated with a higher risk of developing “insulin-requiring” diabetes, according to a study of active-duty servicemembers.
The nested case-control study led by Edward D. Gorham, PhD, MPH, a research epidemiologist from the Naval Health Research Center in San Diego, and assistant adjunct professor in the Department of Family and Preventive Medicine at the University of California, San Diego, was published late last year in the journal Diabetologia.1
Using prediagnostic serum taken as part of a DoD serological surveillance program between 2002 and 2008, researchers compared levels of 25(OH)D of 1,000 consecutive patients who developed insulin-requiring diabetes with 1,000 healthy participants, matched based on “date that the blood sample was drawn (±2 days), age (±3 months), length of military service (±30 days), sex, and whether the control was on active duty when the case was diagnosed,” according to the authors.
All participants were on active duty at the time of the initial blood draw, and most – more than two-thirds – were younger than 35 years old.
Study participants whose vitamin D levels were in the lowest quintile of serum 25(OH)D levels (<43 nmol/L) had a 3.5-fold greater likelihood of developing insulin-requiring diabetes than those in the highest quintile of serum 25(OH)D levels (≥100 nmol/L).
Even those in the second-lowest quintile of serum 25(OH)D levels (43 – 59 nmol/l) had a 2.5-fold greater risk, according to the study, but odds ratios for the next three serum 25(OH)D levels quintiles (60-77, 78-99, and ≥100 nmol/L) were 0.8, 1.1, and 1.0 (reference), respectively.
“Based on the present study, it may be that no further reduction in risk would be expected once a serum 25(OH)D concentration of >60 nmol/l has been attained,” the authors noted.
The servicemembers who developed diabetes had significantly lower mean 25(OH)D levels than the healthy control patients (62.2 nmol/L vs. 72.5 nmol/L; P ≤ .0001).
Although blacks were more likely to develop diabetes than other races represented in the study, the association between 25(OH)D levels and diabetes was seen in all racial groups.
After adjusting for race, study subjects with the lowest quintile of 25(OH)D were at nearly two times greater risk of developing diabetes compared with those in the highest quintile. Compared with whites, the odds ratio for blacks was 1.6.
Noting that worldwide rates of type 1 diabetes vary by latitude, ranging from a low in the tropics (0.5 per 100,000 in Venezuela) to a high near the Arctic Circle (60/100,000 in Finland), researchers suggested that vitamin D could affect immune function.
“Vitamin D deficiency is associated with major effects on the innate immune system. This could potentially influence the risk of diabetes by reducing risk of infection of islet cells,” according to the authors.
Cases were chosen for the study on the basis of insulin dependence, and some study subjects could have had complicated type 2 diabetes, the authors caution.
1. Gorham ED, Garland CF, Burgi AA, Mohr SB, Zeng K, Hofflich H, Kim JJ, Ricordi C. Lower prediagnostic serum 25-hydroxyvitamin D concentration is associated with higher risk of insulin-requiring diabetes: a nested case-control study. Diabetologia. 2012 Dec;55(12):3224-7. doi: 10.1007/s00125-012-2709-8. Epub 2012 Sep 7. PubMed PMID: 22955995.