I only have anecdata and directing you to a search engine. The simple query "magnesium hypertension" yields multiple results going in that direction. Also, magnesium is used to "relax" cells from "contraction" by calcium. Anyway, that's my layman understanding, but magnesium deficiency being at the forefront of an epidemic of "tension" diseases, seems quite evident when you look at the declining nutritional quality in diets, and the increases in stress factors (also depleting magnesium).