Lam Thao, VoPham Trang, Munger Kassandra L, Laden Francine, Hart Jaime E
Graduate School of Life Sciences, Utrecht University, Utrecht, the Netherlands.
Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
Environ Epidemiol. 2020 Jul 6;4(4):e0105. doi: 10.1097/EE9.0000000000000105. eCollection 2020 Aug.
Differences in multiple sclerosis (MS) risk by latitude have been observed worldwide; however, the exposures driving these associations are unknown. Ultraviolet radiation (UV) has been explored as a risk factor, and ambient temperature has been correlated with disease progression. However, no study has examined the impact of all three exposures. We examined the association between these exposures and incidence of MS within two nationwide prospective cohorts of women, the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII).
Both cohorts were followed with biennial questionnaires to ascertain new diagnoses and risk factors. Time-varying exposures to latitude, cumulative average July temperature (°C), and cumulative average July erythemal UV (mW/m) were predicted at each participant's biennially updated residential addresses. Using Cox proportional hazards models adjusted for MS risk factors, we calculated hazard ratios (HR) and 95% confidence intervals (CIs) within each cohort and pooled via meta-analyses.
In multivariable models, there were suggestions that decreasing latitude (meta-analysis multivariable-adjusted HR = 0.72; 95% CI 0.55, 0.94 for women living <35.73° compared with those ≥42.15°, -for-trend = 0.007) and increasing cumulative average July temperature (meta-analysis multivariable-adjusted HR = 0.81; 95% CI 0.72, 0.91 for each interquartile range increase [3.91°]) were associated with decreasing risk of MS. There was no evidence of heterogeneity between cohorts. We did not observe consistent associations with cumulative average UV.
Our results suggest that adult exposures to decreasing latitude and increasing temperature, but not UV, were associated with reduced MS risk in these two cohorts of women. Studies of MS incidence may want to consider temperature as a risk factor.
全球范围内已观察到多发性硬化症（MS）风险因纬度而异；然而，导致这些关联的暴露因素尚不清楚。紫外线辐射（UV）已被探讨为一种风险因素，且环境温度与疾病进展相关。然而，尚无研究考察这三种暴露因素的综合影响。我们在两项全国性女性前瞻性队列研究，即护士健康研究（NHS）和护士健康研究II（NHSII）中，考察了这些暴露因素与MS发病率之间的关联。
两个队列均每两年通过问卷调查随访一次，以确定新的诊断和风险因素。根据每位参与者每两年更新一次的居住地址，预测其随时间变化的纬度暴露、7月累积平均温度（°C）以及7月累积平均红斑紫外线（mW/m）。使用针对MS风险因素进行调整的Cox比例风险模型，我们在每个队列中计算风险比（HR）和95%置信区间（CI），并通过荟萃分析进行汇总。
在多变量模型中，有迹象表明纬度降低（荟萃分析多变量调整后的HR = 0.72；居住纬度<35.73°的女性与≥42.15°的女性相比，95% CI为0.55, 0.94，趋势P值 = 0.007）以及7月累积平均温度升高（荟萃分析多变量调整后的HR = 0.81；每增加一个四分位数间距[3.91°]，95% CI为0.72, 0.91）与MS风险降低相关。队列间无异质性证据。我们未观察到与累积平均紫外线有一致的关联。
我们的结果表明，在这两组女性队列中，成年人暴露于纬度降低和温度升高的环境，但不包括紫外线，与MS风险降低相关。MS发病率研究可能需要将温度视为一种风险因素。
