Night Blood Pressure and Cigarette Smoking: Disparate Association in Healthy Subjects and Diabetic Patients

Cigarette smoking and diabetes are well known risk factors for cardiovascular disease. The relation of nocturnal blood pressure (BP) to cigarette smoking is unclarified. We examined ambulatory BP in 18 healthy smokers matched for sex and age to 18 non-smokers. Sixteen smoking type 1 diabetic patients matching 16 non-smoking patients with normal urinary albumin excretion were also investigated. None of the healthy subjects or diabetic patients had a clinic BP > 160/95 mmHg. Night BP (systolic/diastolic mmHg) in healthy smokers (mean ± SD) 102 ± 9/57 ± 5 was lower than in healthy non-smokers 108 ± 10/61 ± 6 (p = 0.06/p < 0.05). The difference between smokers and non-smokers was most prominent in the 3 h period just before rising (99 ± 9/57 ± 6 versus 108 ± 8/62 ± 7, p < 0.01/p < 0.05). Daytime BP was similar between groups. The night/day ratio (%) of systolic (84 ± 7) and diastolic (74 ± 7) BP in healthy smokers was lower than in non-smokers (88 ± 5 versus 80 ± 5, p < 0.05 and p < 0.01) indicating an altered diurnal rhythm of blood pressure. No statistical significant difference was found for night or day BP in diabetic smokers versus non-smokers. The finding of a significantly lower BP in healthy (supine) smokers at night speaks against dysautonomia explaining the lower clinic BP found in epidemiological studies, as recently proposed. Alternatively a rebound effect or the existence of a substance with vasodilating properties in non-diabetic smokers is suggested. Finally, other potentially confounding life style factors associated with cigarette smoking, may be operative.