LAUSR

To the Editor: The recent article by G. Howard and V.J. Howard reported that the Stroke Belt continues to have the highest stroke mortality rates in the United States and that blacks have higher mortality rates than whites. Their ecological study looked at several well-known risk factors for stroke but did not resolve the issue of black-white disparity. A factor they did not consider is vitamin D status. Blacks have lower 25-hydroxyvitamin D [25(OH)D] concentrations than whites due to dark skin pigmentation. In the period 2001 to 2004, 25(OH)D concentrations for black men and women aged 40 to 59 years were 16 (95% CI, 16–18) and 14 (95% CI, 13–15) ng/mL, respectively. Corresponding concentrations for white men and women were 26 (95% CI, 25–28) and 25 (95% CI, 24–26) ng/mL. An analysis from the REGARDS study (Reasons for Geographic and Racial Differences in Stroke), a cohort of 30 000 black and white adults ≥45 years of age, found 25(OH)D concentrations <20 ng/mL were associated with an incident stroke hazard ratio of 1.85 (95% CI, 1.17–2.93). There were no differences in the 25(OH)D concentration/stroke incidence relationship between blacks and whites. The study by G. Howard and V.J. Howard mentioned that rates of inflammation were higher in the Stroke Belt with CRP (C-reactive protein) and IL (interleukin)-6 concentrations somewhat higher than those in the rest of the United States. A study conducted in Southwest Germany involving 3316 male and female patients (mean±SD age, 63±11 years) found the proinflammatory markers IL-6 and high-sensitivity CRP also decreased considerably with higher 25(OH)D concentrations (P<0.001). After full adjustment, those with optimal serum 25(OH)D >30 versus <10 ng/mL had a reduced odds for fasting diabetes mellitus (OR, 0.63 [95% CI, 0.46–0.86]; P trend, 0.01) and 2-hour postload diabetes mellitus (OR, 0.46 [95% CI, 0.29–0.74]; P trend, 0.004). An intervention study was conducted involving 53 patients of acute ischemic stroke with serum 25(OH)D concentration <30 ng/mL. They were randomized into 2 arms: 25 received a single intramuscular injection of 600 000 IU of vitamin D3 followed by 60 000 IU oral vitamin D3 once a month with 1 g of elemental calcium daily along with usual poststroke care. The control arm had 28 patients who received usual poststroke care. Four deaths occurred in the treatment arm, and 11 deaths occurred in the control arm by the end of 100 days, although the study ran for 180 days. The survival outcome had an adjusted hazard ratio of 0.26 (95% CI, 0.08–0.90) in favor of treatment. While these were overall deaths, most of them were probably due to ischemic stroke. Thus, there is reasonable evidence that lower 25(OH)D concentrations for blacks compared with whites explain the racial disparity in stroke mortality rates observed. Whether it also helps explain the higher stroke mortality rates in the Stroke Belt than elsewhere in the United States is an open question. Factors in addition to skin pigmentation that affect 25(OH)D concentrations include higher body weight, smoking, air pollution, indoor occupation, the vitamin D content of food, and whether vitamin D supplements are being taken. Perhaps the authors G. Howard and V.J. Howard can address these issues in their further research.