March 06, 2020
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UVA, UVB exposure may lower BP in dialysis, regardless of outside temperature

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Richard B. Weller

Patients undergoing dialysis experienced significant BP reduction when exposed to solar ultraviolet radiation, regardless of environmental temperature. The decrease in BP was greater in the presence of ultraviolet B radiation compared with ultraviolet A, according to research published in the Journal of the American Heart Association.

Among 342,457 patients receiving dialysis at 2,178 centers across the U.S. (mean age, 59 years; 57% men; 36% black; 67% with hypertension), researchers observed significant systolic BP reduction associated with change in UVA (white patients, –0.75 mm Hg; 95% CI, –0.78 to –0.72; black patients, –0.63 mm Hg; 95% CI, –0.66 to –0.59).

Moreover, UVB exposure appeared to have a stronger effect on systolic BP (white patients, –12.73 mm Hg; 95% CI, –13.22 to –12.23; black patients, –10.49 mm Hg; 95% CI, –11.07 to –9.91) compared with UVA exposure.

These findings remained significant after adjustment for environmental temperature:

  • UVA exposure (white patients, –0.32 mm Hg; 95% CI, –0.37 to –0.27; black patients, –0.23 mm Hg; 95% CI –0.29 to –0.16); and
  • UVB exposure (white patients, –5.63 mm Hg; 95% CI, –6.48 to –4.78; black patients –4.17 mm Hg; 95% CI, –5.26 to –3.08).

“UVA (320-400 nm), the predominant form of UV reaching the earth’s surface, will partly pass through window glass and penetrate as deep as the dermis in skin. Although not absorbed by DNA (and thus not directly mutagenic), it is absorbed by other photosensitizers and consequently generates free radicals, producing oxidative stress,” the researchers wrote. “UVB (280-320 nm) is responsible for the photochemical synthesis of pre-vitamin D3 from 7-dehydrocholesterol but is also a direct DNA mutagen. It makes up approximately 5% of incident UV radiation, and is around two orders of magnitude more erythemogenic than UVA.”

Using solar UV radiation and temperature data from the National Oceanic and Atmospheric Administration database, researchers assessed the relationship between environmental factors and mean BP in patients undergoing dialysis. Patients were followed up for approximately 12 months and mean predialysis BP was 146.84 mm Hg.

We've known for many years that BP is lower in summer than winter and it's been assumed that this is due to either warmer temperatures or vitamin D. Results of meta-analyses published in the last two or three years have shown that vitamin D has absolutely no effect on blood pressure,” Richard B. Weller, MD, academic dermatologist at the MRC Centre for Inflammation Research at University of Edinburgh, U.K., told Healio. “In this observational study with a huge dataset in which we could cross-reference UV (of various wavelengths), temperature, skin color and patient factors against BP, we have been able to show for the first time that independently of temperature, more UV correlates with lower BP.”

Future research on UV risk-benefit

“Conclusive proof that UV was carcinogenic to skin was produced in 1928 (Findlay GM, et al. Lancet. 1928;doi:10.1016/S0140-6736(00)84845-X.),” Weller said in an interview. “The intervening century has been spent researching almost entirely the adverse effects of sunlight, with no consideration for benefits, and yet we still don’t even have a dose-response curve for environmental UV and any form of skin cancer. For melanoma it is even more confusing — epidemiological data suggest that chronic sun exposure (being an outdoor worker and being tanned) may be protective. My work — including a clinical trial of UVA phototherapy to treat early hypertension — is beginning to generate data on how much UV is needed to give a defined fall in BP with the benefits expected from this.” by Scott Buzby

Disclosures: Weller reports he is on the advisory board of AOBiome LLC and Relaxsol Ltd. Please see the study for all other authors’ relevant financial disclosures.