ACADEMY PUBLIC POLICIES

Salt intake

I have always put salt on my food. I am now told that I have to cut this out. Will this be an effective way of lowering my BP?

The relationship between salt intake and BP levels is a contentious and controversial subject. Population studies comparing the effects of consumption of salt and BP in different countries or regions have shown clearly that, in countries where there is greater average salt intake, there is a higher risk of stroke and other cardiovascular disease.

High BP does not exist at all, nor does average BP rise with age, in some tribes in Brazil and Papua-New Guinea where salt intake is at the bare minimum essential for life (less than 15 mmol sodium a day), about one-tenth of the present average intake in the UK (about 150 mmol a day). On the other hand, in countries with very high sodium intakes, such as rural Portugal where average sodium intake is about twice that in the United Kingdom (300 mmol a day), or rural northern Japan where the intake is more than two and a half times the UK intake (400 mmol a day), both high BP and stroke are extremely common.

Studies show that, compared to usual diet, low-salt diets modestly reduce BP levels in the region of 1–2 mmHg systolic and 0.5 mmHg diastolic BP. In these studies of salt reduction, very few people have been followed up to see whether they suffer later from a heart problem; thus all the information relates to BP control rather than probability of suffering a stroke or heart attack.

Another issue is that the changes in salt intake in some of these studies were very intensive, requiring substantial alteration in the usual diet. Whether such changes in diet can be sustained outside of clinical trial settings is the subject of different opinions in the high BP research community. The main recommendation is that reducing salt intake is worthwhile, particularly in the elderly or those people already taking BP-lowering drugs. Reduction of salt intake in conjunction with changes in diet and increasing exercise may allow some people to achieve a sufficient reduction in their BP to allow them to stop taking BP-lowering drugs. However, this assumes that reductions in salt are not accompanied by a rise in fat intake. This may happen easily if low-salt food seems tasteless.

How should I go about modifying the salt intake in my diet?

The main source of sodium in most foods is sodium chloride, ordinary salt. This is present not only in added cooking salt or table salt, but also in such usually unsuspected high-sodium foods as milk, cheese and bread and in virtually all tinned or ready prepared foods such as most breakfast cereals, sausages, burgers, pizzas and soups. A diet sufficiently low in sodium to reduce BP, with sodium intake reduced to about half normal at 60–70 mmol day, must virtually eliminate all these foods, as well as more obvious ones like kippers, bacon, olives, hummus and Marmite. There are two secrets of successful reduction of dietary sodium:

• The first is to reduce salt intake slowly, taking 3 months or more to reach your target. After a few months you find that your sense of taste has more or less permanently changed, and normally salted foods become quite unpleasant.

Although there will still be many delicious foods that you cannot eat, what you can eat will (eventually) start to taste good again.

• The second secret is to include the whole family in the diet, so that the whole meal can be cooked in the same way. As high BP runs so strongly in families, this is a good idea anyway.

If you follow a moderately low-sodium diet of this kind, and if you have mildly raised BP in the diastolic range 90–95 mmHg, you may not need any medication. If it is much higher than this, you may need lower doses, or fewer different drugs, than you would on your usual diet. A dietitian will be able to help you adjust your salt intake.