|MadSci Network: General Biology|
Firstly the effects of alcohol on human heart rate are not due to direct effects on the heart, but due to the activation of a reflex response. Alcohol is a vasodilator, which means that it makes the peripheral blood vessels relax allowing more blood to flow through the skin and tissues. This is why people who have had a drink look red faced and feel warm. This means that the blood flows round a larger volume of the body, which results in a drop in blood pressure. Therefore, to maintain sufficient blood flow through the organs of the body the heart rate increases to accommodate for the increased volume that it has to send the blood round.
A number of recent studies have found that there is a slight reduction in the rate of people who have one or two drinks a day, compared with people who drink either nothing or three or more drinks per day. It seems that this reduction in moderate drinkers is because alcohol consumption decreases the incidence of coronary heart disease. (The heart has its own network of arteries that supply the muscle with blood and sometimes people get restrictions and blockages in these arteries). At least half of this association is because alcohol increases the levels of HDL (high density lipoproteins), which remove cholesterol from the arterial wall and back to the liver. Other reasons for this effect may be that alcohol may slightly reduce the clotting capacity of the blood, a so called 'thinning' of the blood, which can also protect against coronary heart disease.
For people that drink more that one or two drinks per day the beneficial effects of a small amount of alcohol are offset by the more harmful effects of alcohol, which include stroke, several kinds of cancer, cirrhosis and pancreatitis as well as accidents, suicide and homicide.
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