MS Sunshine Study: Sun Exposure But Not Vitamin D Is Associated with Multiple Sclerosis Risk in Blacks and Hispanics

Abstract

Multiple sclerosis (MS) incidence and serum 25-hydroxyvitamin D (25OHD) levels vary by race/ethnicity. We examined the consistency of beneficial effects of 25OHD and/or sun exposure for MS risk across multiple racial/ethnic groups. We recruited incident MS cases and controls (blacks 116 cases/131 controls; Hispanics 183/197; whites 247/267) from the membership of Kaiser Permanente Southern California into the MS Sunshine Study to simultaneously examine sun exposure and 25OHD, accounting for genetic ancestry and other factors. Higher lifetime ultraviolet radiation exposure (a rigorous measure of sun exposure) was associated with a lower risk of MS independent of serum 25OHD levels in blacks (adjusted OR = 0.53, 95% CI = 0.31–0.83; p = 0.007) and whites (OR = 0.68, 95% CI = 0.48–0.94; p = 0.020) with a similar magnitude of effect that did not reach statistical significance in Hispanics (OR = 0.66, 95% CI = 0.42–1.04; p = 0.071). Higher serum 25OHD levels were associated with a lower risk of MS only in whites. No association was found in Hispanics or blacks regardless of how 25OHD was modeled. Lifetime sun exposure appears to reduce the risk of MS regardless of race/ethnicity. In contrast, serum 25OHD levels are not associated with MS risk in blacks or Hispanics. Our findings challenge the biological plausibility of vitamin D deficiency as causal for MS and call into question the targeting of specific serum 25OHD levels to achieve health benefits, particularly in blacks and Hispanics.

Environmental and genetic risk factors for MS: an integrated review

“…Observational studies similarly show that lower 25OHD levels are associated with increased MS risk in White populations . A similar association is not seen in Hispanics and Blacks . Within White populations, the dose–response relationship is inconsistent; for example, both threshold (e.g.…”

“…These inconsistent associations may be because few studies have accounted for sun exposure. Where data are available on both sun exposure and 25OHD levels, there are statistically independent benefits of higher levels of either in Whites . Both UV radiation and vitamin D have effects on innate and adaptive immune function that would plausibly be beneficial for MS …”

Low sun exposure increases multiple sclerosis risk both directly and indirectly

“…Sun exposure is the principal source of vitamin D and evidence indicates a protective role for higher vitamin D levels [19,20]. However, a multi-ethnic study observed that sun exposure reduced the risk of MS regardless of race/ethnicity, whereas vitamin D deficiency was only associated with MS risk among whites [21]. Several studies have reported that sun exposure and vitamin D are independently associated with decreased MS risk [10,22].…”

On the Nature of Evidence and ‘Proving’ Causality: Smoking and Lung Cancer vs. Sun Exposure, Vitamin D and Multiple Sclerosis

“…This lack of consistency for 25(OH)D levels across races seems biologically implausible, but may be explained by the weaker correlation between recent sun exposure and 25(OH)D levels in darker skinned, compared to lighter skinned, individuals [33], i.e., 25(OH)D reflects recent sun exposure, rather than vitamin D per se. Nevertheless, a nested case-control study within a large cohort study showed that higher total vitamin D intake (from diet and supplements, when supplements were assumed to contain 400 IU of vitamin D) was associated with reduced risk of MS [44].…”