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(Hypertension. 1998;31:719.)
© 1998 American Heart Association, Inc.

Letters to the Editor

Ultraviolet Light May Contribute to Geographic and Racial Blood Pressure Differences

Christopher Bell

Faculty of Health Sciences, Department of Physiology, Trinity College Dublin, Ireland

To the Editor:

Dr Rostand's recent article¹ draws attention to a fascinating but hitherto-neglected result of the INTERSALT study: that population mean blood pressures and the incidence of hypertension both appear to be positively correlated with the latitude north or south of the equator at which the population lives. Dr Rostand notes that geographical movement away from the equator is associated with a fall in ambient ultraviolet radiation. Decreased ultraviolet radiation reduces vitamin D synthesis, and this can elevate parathyroid hormone levels; furthermore, parathyroid hormone can stimulate vascular wall growth. Drawing from these data and published evidence for altered calcium homeostasis in human hypertensive subjects, Rostand postulates that the variation in blood pressure with latitude may therefore be linked to the different intensities of ambient ultraviolet light.

Dr Rostand's proposal is an attractive one, serving as it does to pull together many disparate strands of the complex fabric that seems to underlie the genesis of essential hypertension. It has important potential implications for our interpretation of the role of calcium in hypertension and may offer valuable clues to the understanding of racial differences in salt sensitivity and renin profiles and of different racial susceptibilities to high blood pressure.

There is, however, an additional mechanism by which ambient electromagnetic radiation may reduce blood pressure. Robert Furchgott and his colleagues noted as long ago as 1961 that exposure to light relaxed isolated arterial preparations,² although other types of smooth muscle tissue were much less sensitive.³ The vascular photorelaxation was wavelength dependent, increasing . . . [Full Text of this Article]

Stephen G. Rostand

Nephrology Research and Training Center, Division of Nephrology, University of Alabama at Birmingham, Birmingham, Ala