Nutritional advice

Alcohol intake is emerging as one of the important environmental factors associated with raised blood pressure.Heavy drinkers have higher blood pressure than light drinkers and abstainers. The effect starts above about three (stated) drinks a day. Systolic pressure is more affected than diastolic.The pressor effect of alcohol can be demonstrated directly.It was seen, for example, in men with essential hypertension who were moderate to heavy drinkers. They continued their habitual intake of beer and antihypertensive drugs; when low alcohol beer (0.9% alcohol) was substituted for the same intake of regular beer (5% alcohol), their blood pressure fell 5/3mmHg. The mechanism(s) have not yet been established.Acute ingestion of alcohol causes peripheral vasodilatation, but there are features of a hyperadrenergic state in the withdrawal syndrome. Plasma cortisol concentrations are sometimes raised in alcoholics. Increased red cell volume, and hence increased blood viscosity, is a possible mechanism

Obese people are likely to have a higher blood pressure than lean people. In a cohort of over 5000 people born in Britain in the same week, blood pressures at the age of 36 were progressively higher in those with a body mass index (weight (kg)/height (m2)) above 26. Typically a 3 mmHg higher diastolic pressure may be expected for every 10 kg increase in body weight.In a large Swedish study of 60-year-old men, a quarter of the fattest fifth were taking antihypertensive drugs compared with only 4% of the thinnest fifth.Raised blood pressure and hyperlipidaemia are both major risk factors for cardiovascular disease, and effective weight reduction will improve both.

• People who do not eat enough food energy and lose weight usually have a fall of (normal) blood pressure.
• If hypertensive obese patients reduce their weight they show falls of blood pressure like 10 mmHg systolic/5 mmHg diastolic for a 5-kg weight loss.
• Less food means less sodium eaten. Some weight loss occurs even if sodium intake is maintained, but the combination of weight loss and a low sodium intake is more effective.
• In a randomised placebo-controlled trial of first-line treatment of mild hypertension in overweight patients, the weight reduction group (mean loss 7.4 kg) had a 13 mmHg fall of systolic blood pressure while those treated with metoprolol (200 mg/day) had a 10 mmHg fall.

Most of the salt that we eat is not that added at the table or in cooking water (much of which goes down the sink). It is salt added in food processing, particularly of staple foods. Wheat flour contains 3 or 4 mg sodium/100 g but average breads have 520-550 mg/100 g. Oils like sunflower or olive oil contain only traces of sodium but butter averages 750 mg/100 g and margarines 800 mg/100 g. Many cereal products—biscuits, cakes and breakfast cereals (though not all)—are very high in sodium, which consumers cannot taste (being masked by the sugar content). Salted peanuts contain less sodium than breads; consumers can taste the salt because it is all on the surface. Anyone wanting to reduce salt intake must find low-salt breads and breakfast cereals and cheeses as well as cutting out the more obvious bacon and olives in brine which people eat less often. Other sodium compounds in food, bicarbonate and glutamate, have less effect on blood pressure than sodium chloride.

Elevated blood pressure can usually be lowered by salt restriction.Diuretic drugs work by increasing urinary sodium excretion. Alternatively a sufficient reduction of dietary sodium can achieve the same degree of negative sodium balance. In mild to moderate hypertension, a reduction of sodium intake (which can be monitored with 24-hour urinary sodium) by 50 mmol/day will usually give a useful reduction of blood pressure, so that the patient may be able to come off the hypotensive drugs (or not start them) or reduce the dose (and with this the probability of side effects). Salt restriction increases sensitivity to all hypertensive drugs except slow channel calcium blockers, like nifedipine. Some people are more responsive than others. Older people may be more responsive to salt reduction and they are particularly susceptible to the side effects of drugs. When people change to a lower salt diet their taste adjusts after a few weeks. Other flavours are perceived and appreciated more. The major obstacle to eating low salt is that most of the salt in food is put in during processing and is outside the individual’s control.

Salt (sodium)

Hypertension is not an inevitable accompaniment of ageing. Evidence showed that hypertension did not occur in a few isolated communities, such as Yanomamo Indians (in the Amazon), Kalahari Bushmen (Botswana), and remote Pacific islanders. These people typically had no access to salt and their urinary sodiums (reflecting salt intake) were under 30 mmol/day. The requirement for sodium in health is usually under 25 mmol Na/day (equivalent to 1.5 g NaCl).9 Normal kidneys can shut down sodium excretion almost to zero and sweat loss is reduced in people on low salt intakes or adapted to hot climates. Human milk contains only 7 mmol Na/litre, so young infants’ sodium intake per megajoule is only about one-sixth that of their parents’!