Vascular function and structure is maintained or improved by long term administration of physiologically acceptable compounds, namely L-arginine, L-lysine, physiologically acceptable salts thereof, and polypeptide precursors thereof, which enhance the level of endogenous nitric oxide or other intermediates in the NO induced relaxation pathway in the host. In or in combination, other compounds, such as B.sub.6, folate, B.sub.12, or an antioxidant, which provide for short term enhancement of nitric oxide, either directly or by physiological processes may be employed.