Solar UV Radiation: A Potential Modifiable Risk Factor for Hypertension

Vikas Kapil, Ajay K. Gupta
2020 Journal of the American Heart Association : Cardiovascular and Cerebrovascular Disease  
I ncreased blood pressure (BP) is one of the leading risk factors for cardiovascular morbidity and mortality worldwide, eclipsing smoking and alcohol, with the lowest risk associated with a usual systolic BP (SBP) between 110 and 115 mm Hg, well within the normotensive range. 1 BP is regulated by a myriad of endogenous (eg, neural, cardiac, and endocrine) and exogenous (eg, diet and exercise) factors that can adversely serve to lead to hypertension and excess cardiovascular risk. Currently,
more » ... isk. Currently, treatment strategies to reduce BP and subsequent cardiovascular risk are underpinned by various pharmacological approaches. However, despite the availability of numerous antihypertensive agents (and easy availability of their cheap generic versions), BP control at population level seems to be elusive, even in the resource-rich western world. 2 On the other hand, public health strategies promoting diet and exercise to prevent and manage hypertension have not shown desired results either; almost all guidelines emphasize lifestyle modifications, particularly dietary and exercise-based interventions, in conjunction with antihypertensive agents. 3 This focus on dietary and exercise-type advice is in part because of the relative ease with which these 2 interventions are amenable to design and conduct of clinical trials, although there are clearly challenges to such trials, such as blinding and adherence to intervention. However, there are protean environmental factors associated with increased BP that may also be amenable to modification through population strategies to lower excessive cardiovascular risk related to BP, including ambient noise and atmospheric pollution, among others. 4 Further atmospheric conditions (namely, ambient air temperature) have long been known to be associated with seasonal variation in usual BP 5 that constitutes one of the long-term patterns of BP variability, both measured in the office and out of office. 6 The mechanisms relating to these seasonal associations of BP and ambient temperature have been proposed to include cold-induced sympathetic-induced vasoconstriction and renin-angiotensin-aldosterone system activation, 7 among others. However, interpretation of epidemiological data is confounded by daily sunlight (ie, there are longer daytime solar hours in summer). This therefore invokes the possibility that it is solar exposure rather than (or more likely, in synergy with) ambient temperature that is mechanistically important for BP regulation. Indeed, for much of the past 20 years, extensive research has been performed to determine whether vitamin D, which is produced in the skin in response to solar radiation exposure, is important in BP regulation. Large observational studies have shown that low vitamin D levels are a risk factor for hypertension, 8 although conversely meta-analysis of numerous vitamin D intervention trials has shown no overall benefit on BP. 9 To date, no large data set combined solar radiation exposure and ambient temperature to tease out the relative importance of one or other of these mechanisms for BP regulation. In this issue of the Journal of the American Heart Association (JAHA), Weller and colleagues 10 have used an extremely large data set of 340 000 patients from >2000 hemodialysis centers in the United States, covering extremely different geographies and environmental conditions, with >45 million predialysis BP records. They used 2-stage analysis: mixed effect model for repeated measures at each center level and combining these individual center-level records using random-effects meta-analysis models, to evaluate the relative importance of UV light exposure and daily average temperature at the locality of each center. 10 The major finding of the study is that UV radiation intensity is inversely related to predialysis SBP independent of ambient temperature, although there appeared to be an interaction
doi:10.1161/jaha.120.015627 pmid:32106745 fatcat:4o6trys7vrapjebluavuajoyqi