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Clinical Review ABC of alcohol

Alcohol in the body

BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7482.85 (Published 06 January 2005) Cite this as: BMJ 2005;330:85
  1. Alex Paton

Introduction

Alcohol (ethanol) is a drug, and health professionals should know something of its physiological and pathological effects and its handling by the body. It is a small, water soluble molecule that is relatively slowly absorbed from the stomach, more rapidly absorbed from the small intestine, and freely distributed throughout the body. Alcoholic drinks are a major source of energy—for example, six pints of beer contain about 500 kcal and half a litre of whisky contains 1650 kcal. The daily energy requirement for a moderately active man is 3000 kcal and for a woman 2200 kcal.

Absorption

Rate of absorption of alcohol depends on several factors. It is quickest, for example, when alcohol is drunk on an empty stomach and the concentration of alcohol is 20-30%. Thus, sherry, with an alcohol concentration of about 20% increases the levels of alcohol in blood more rapidly than beer (3-8%), while spirits (40%) delay gastric emptying and inhibit absorption. Drinks aerated with carbon dioxide—for example, whisky and soda, and champagne—get into the system quicker. Food, and particularly carbohydrate, retards absorption: blood concentrations may not reach a quarter of those achieved on an empty stomach. The pleasurable effects of alcohol are best achieved with a meal or when alcohol is drunk diluted, in the case of spirits.


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Rate of absorption of alcohol (arrows) is affected by concentration of alcohol

Alcohol is distributed throughout the water in the body, so that most tissues—such as the heart, brain, and muscles—are exposed to the same concentration of alcohol as the blood. The exception is the liver, where exposure is greater because blood is received direct from the stomach and small bowel via the portal vein. Alcohol diffuses rather slowly, except into organs with a rich blood supply such as …

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