BLOOD pressure (BP) continues to be an important determinant of our health and has significant implications for many diseases including stroke, heart disease, kidney damage and eye disease. Understanding how our lifestyles impact our blood pressure can help us make the right decisions in maintaining a healthy range of BP.
Normal BP fluctuation
There is a diurnal physiological variation in BP, which rises on wakening in the early morning when the person gets up, reaches a plateau during the morning, decreases slightly in the early afternoon and rises again in the early evening. The BP then decreases gradually in the late evening, drops sharply after falling asleep and is lowest during sleep at about 3am. The BP increases again by about 20 per cent between 6am and 8am, around the time of awakening. If the sleep-time relative systolic blood pressure (SBP) decline is 10 per cent or more, this sleep pattern is considered a normal dipper pattern. In the majority of normotensive persons, the decrease in BP from daytime to night time is about 10 per cent to 20 per cent.
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.
Morning BP surge
The typical physiological morning elevation in BP is more a function of activity rather a function of the time of the day. Those who remain supine in bed after waking up do not show much change in their BP, which rises rapidly only when the person gets upright. The extent of BP elevation is related to the level of physical activity. In some patients with hypertension, an exaggerated increase in BP is seen and this is termed the morning surge.
Upon awakening and getting up and commencing activities of daily living, there is a large surge in your “fight or flight” hormones, namely the catecholamines (such as adrenaline). This results in increase in heart rate, increase in BP, greater pumping action of the heart, increase in your arterial vessel tone and decrease in the calibre of the arteries.
Other awakening changes include an increase in your body steroids (cortisol) level, and “thickening” of the blood (due to increased tendency of the platelets to stick together and an increase in blood viscosity). These changes result in an increased demand for oxygen by the heart, decrease in oxygen supply to the heart and “thickening” of the blood. These changes may help to explain the increase in heart and stroke events during the morning. 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. In addition to the morning surge, hypertensive patients tend to have no dip in BP (non-dipping) at night. The nighttime non-dipping is associated with damage to key organs (such as the heart, brain and kidney) and heart disease.
Stress and BP
As everyone knows, stress increases BP. The stress of doing housework or rushing to work in the morning may cause an exaggerated surge in morning BP and even morning hypertension. Workplace stress can also cause daytime hypertension. A study reported that more than 20 per cent of civil servants who had workplace hypertension had normal BP during health examination. Interrupted sleep results in elevated BP and may contribute to the non-dipping of BP at night. It has been shown that hospitalisation can reduce stress, resulting in lower BP in the day and reduced difference between daytime and night-time BP in hypertensives. Activities such as meditation can also lower BP effectively.
Lifestyle and BP
There is little surprise that obese individuals have higher BP values than normal individuals. The good news is that weight loss in hypertensives can result in reduction in BP. 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 nighttime BP.
During exercise, BP increases and post-exercise, it decreases. This post exercise drop is due to a relaxation of the tone of the blood vessels and usually lasts for several hours. Several studies have also shown that regular exercise lowers BP in both normotensives and hypertensives. The impact of exercise on BP is dependent on the time of exercise, with morning exercise resulting in decrease in daytime BP and evening exercise decreasing night-time BP in non-dippers (hypertensive pattern), but not dippers (normal pattern).
Taking a hot shower usually causes a rise in BP initially, but if you are immersed in a hot bath, BP will decrease with even further decrease immediately after the bath. It will gradually return to the baseline levels after about one hour. For smokers, studies using ambulatory BP monitoring have shown that only daytime BP is elevated, and it is higher on smoking than on nonsmoking days. Therefore, chronic smoking can cause daytime hypertension.
Food and BP
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. This post-prandial drop in BP is minor in the young but may be more pronounced in the elderly, in hypertensives, and following a high-carbohydrate meal (as compared to high-fat meal).
The peak of the post-prandial reduction in BP is at about one hour and persists for more than two hours. It is a well-known fact that a high sodium intake increases BP and a low sodium intake can decrease it. In contrast, dietary intake of potassium and magnesium is inversely related to BP. Hence, the consumption of fruits and vegetables that are rich in potassium and magnesium may decrease BP in hypertensives. Coffee lovers may be surprised to know that consumption of coffee can transiently increase the BP by up to 10 mm Hg for about one hour. Much of this is believed to be due to the effects of caffeine on the body. Conversely, the consumption of cocoa or dark chocolate appears to be associated with a significant reduction in 24 hours’ BP.
Shedding excess weight by exercising, followed by a hot bath immersion, consumption of dark chocolate, fruits and vegetables (high in magnesium and potassium) and ending the day with stress-relieving meditation is a perfect recipe for lowering the blood pressure. In addition, reducing salt, coffee, excessive weight, smoking and stress will certainly help you achieve the ideal BP and ultimately a healthy life.