While many may think that this is due to your internal body clock, in truth, the variation associated with the sleep wake cycle is largely influenced by mental and physical factors. Hence, in shift workers, BP is high during work at night and low during sleep in the day.The typical physiological morning elevation in BP is more a function of activity rather a function of the time of the day.
Analysis of combined trial data has demonstrated an approximately 40 per cent increase in incidence of heart attacks, close to 30 per cent increase in incidence of heart-related deaths and close to 50 per cent increase in incidence of stroke, as compared to other periods of the day. Many obese individuals have obstruction of their upper airway resulting in snoring and a condition called obstructive sleep apnoea. This decrease in oxygen delivery to the body as a result of airway obstruction during sleep is associated with an increase in night-time BP.
For smokers, studies using ambulatory BP monitoring have shown that only daytime BP is elevated, and it is higher on smoking than on non-smoking days. Therefore, chronic smoking can cause daytime hypertension.It has been observed that there is a mild increase in BP during meals as a result of increased physical activity, followed by a fall after meals as a result of dilatation of the vessels in the gut in response to food consumption.