The fact that most MAs on results from RCTs did not show a beneficial effect does not disprove the hypothesis suggested by observational findings on adverse health outcomes of low 25OHD levels
Background A large number of observational studies have reported harmful effects of low 25-hydroxyvitamin D ( 25OHD ) levels on non-skeletal outcomes .
We performed a systematic quantitative review on characteristics of r and omized clinical trials ( RCTs ) included in meta-analyses ( MAs ) on non-skeletal effects of vitamin D supplementation .
Plasma 25-Hydroxyvitamin D Levels and Risk of Incident Hypertension
Hydroxylation of 25(OH)D to 1,25-dihydroxyvitamin D and signaling through the vitamin D receptor occur in various tissues not traditionally involved in calcium homeostasis . Laboratory studies indicate that 1,25-dihydroxyvitamin D suppresses renin expression and vascular smooth muscle cell proliferation ; clinical studies demonstrate an inverse association between ultraviolet radiation , a surrogate marker for vitamin D synthesis , and blood pressure . We prospect ively studied the independent association between measured plasma 25-hydroxyvitamin D [ 25(OH)D ] levels and  risk of incident hypertension  and also the association between predicted plasma 25(OH)D levels and risk of incident hypertension .  Two prospect i ve cohort studies including 613 men from the Health Professionals ’ Follow-Up Study and 1198 women from the Nurses ’ Health Study with measured 25(OH)D levels were followed for 4 to 8 years . In addition , 2 prospect i ve cohort studies including 38 388 men and 77 531 women with predicted 25(OH)D levels were followed for 16 to 18 years . During 4 years of follow-up , the multivariable relative risk of incident hypertension among men whose measured plasma 25(OH)D levels were < 15 ng/mL ( ie , vitamin D deficiency ) compared with those whose levels were ≥30 ng/mL was 6.13 ( 95 % confidence interval [ CI ] : 1.00 to 37.8 ) . Among women , the same comparison yielded a relative risk of 2.67 ( 95 % CI : 1.05 to 6.79 ) . The pooled relative risk combining men and women with measured 25(OH)D levels using the r and om-effects model was 3.18 ( 95 % CI : 1.39 to 7.29 ) . Using predicted 25(OH)D levels in the larger cohorts , the multivariable relative risks comparing the lowest to highest deciles were 2.31 ( 95 % CI : 2.03 to 2.63 ) in men and 1.57 ( 95 % CI : 1.44 to 1.72 ) in women . Plasma 25(OH)D levels are inversely associated with risk of incident hypertension
The fact that most MAs on results from RCTs did not show a beneficial effect does not disprove the hypothesis suggested by observational findings on adverse health outcomes of low 25OHD levels
Background A large number of observational studies have reported harmful effects of low 25-hydroxyvitamin D ( 25OHD ) levels on non-skeletal outcomes .
We performed a systematic quantitative review on characteristics of r and omized clinical trials ( RCTs ) included in meta-analyses ( MAs ) on non-skeletal effects of vitamin D supplementation .