Vitamin D status and coronary flow reserve measured by positron emission tomography: a co-twin control study.
CONTEXT
Vitamin D insufficiency is associated with increased cardiovascular events in the general population. Additionally, low serum 25-hydroxyvitamin D [25(OH)D] is associated with endothelial dysfunction and arterial stiffness. However, little is known about the association between serum 25(OH)D level and myocardial blood flow.


OBJECTIVE
Our objective was to examine the association between serum 25(OH)D levels and coronary flow reserve (CFR) measured by (13)N-positron emission tomography in asymptomatic middle-aged male twins.


DESIGN
The Emory Twin Study is a cross-sectional study of soldiers from the Vietnam Era Registry.


SETTING
The study was conducted at the General Clinical Research Center, Emory University, Atlanta, GA.


PARTICIPANTS
A total of 368 middle-aged male twins were enrolled for the study. Serum 25(OH)D levels were measured in all subjects and classified as vitamin D insufficiency [25(OH)D <30 ng/ml] or sufficiency [25(OH)D ≥30 ng/ml]. Positron emission tomography with [(13)N]ammonia was used to evaluate myocardial blood flow at rest and after adenosine stress. CFR was measured as the ratio of maximum to rest myocardial blood flow.


MAIN OUTCOME MEASURE
Primary outcome was CFR measurement.


RESULTS
Mean overall serum 25(OH)D concentration was 37.0 ± 21.4 ng/ml; 167 twins (45%) were vitamin D insufficient. CFR was significantly lower in subjects with vitamin D insufficiency compared with subjects with vitamin D sufficiency (2.41 vs. 2.64; P = 0.007), even after adjustment for traditional cardiovascular risk factors, serum PTH, calcium, and phosphorus levels, and season. An abnormal CFR (CFR <2) was more prevalent in subjects with vitamin D insufficiency than with vitamin D sufficiency (31 vs. 20%; P = 0.03). In addition, in vitamin D status-discordant twin pairs, CFR was significantly lower in the vitamin D-insufficient twin than in the vitamin D-sufficient co-twin (2.35 vs. 2.58; P = 0.037).


CONCLUSION
Vitamin D insufficiency is associated with lower CFR in men. This association may help explain some of the increased cardiovascular risk reported in individuals with vitamin D insufficiency.