Hypertension is a major public health epidemic all over the world, with increasing prevalence. Nearly seven million deaths worldwide are attributed to high blood pressure (BP) each year. Hypertension has been found to be a risk factor for ischemic heart disease, stroke, cardiac and renal failure 1 . In recent years it has been discovered that short sleep duration and poor quality of sleep greatly increase the risk for developing high blood pressure, which in turn increases related risks.
Blood pressure and the biological clock
Blood pressure and sleep, as well as other physiological body functions such as alertness, hormone levels, body temperature etc., have a 24 hr cycle (the body’s biological clock). This clock is controlled by various environmental signals; most importantly the light–dark cycle and melatonin (the “sleep hormone”) which is in charge of sleep regulation and the circadian clock. Normal blood pressure (BP) varies across 24 hr, with daytime pressures being higher than night time pressures. Normally, in healthy people, blood pressure should drop down at about 10% relative to a daytime baseline, especially in the second part of the night. This pattern is called “dipping”. people who fail to show lower night time BP of at least 10% relative to daytime BP are called “nondippers” 2 . Evidences suggest that persons with a “non-dipping” pattern are at higher risk for cardiovascular morbidity and mortality than those with a “dipping” pattern.
Sleep and blood pressure regulation
Studies show that suboptimal sleep (duration and quality) is associated with higher BP. Patients with hypertension are 2-3 times more likely to have insomnia than patients with normal blood pressure and vise-versa 3 . It was found that ‘Non-dipping’ people had less deep sleep (less quality sleep), more light sleep and a greater percentage of awakenings during the night 2 . Sleep deprivation has been observed to be related to significant increases in BP, where improving sleep duration and quality can help with reduction of both daytime and nighttime BP levels 4 .
Melatonin and blood pressure regulation
Melatonin was found to play an important role in blood pressure regulation. Researchers showed that removal of the pineal gland (where melatonin is produced) or continuous exposure to light resulted in melatonin deficiency and high blood pressure (hypertension) 5 . It was also found that ‘Non-dippers’ tend to produce less melatonin. Furthermore, beta-blockers, a common anti-hypertensive drug, were found to reduce melatonin secretion, resulting in insomnia 6 . Moreover, although treatment with anti-hypertensive drugs generally lowers daytime blood pressure, it does not completely abolish nighttime ‘Non-dipping’ phenomenon. This indicates that drugs for high blood pressure do not properly restore the Circadian rhythm (body’s biological clock) of blood pressure and therefore the risk for cardiovascular events in such people remains high 7 . Studies show that repeated melatonin intake (mainly prolonged release melatonin) not only improves sleep quality in patients with high blood pressure who are treated with beta-blockers6, but also reduces nocturnal blood pressure 1 8 .
Therefore, treatment with melatonin may simultaneously handle both insomnia and high blood pressure and may help in the regulation of the blood pressure rhythm and reducing the cardiovascular mortality and morbidity risk in hypertensive patients with insomnia.