There is tremendous controversy about how important salt intake really is in causing high blood pressure, heart attacks and strokes. Data show that moderate salt restriction can lower high blood pressure, severe salt restriction raises high blood pressure. If you are an exerciser and restrict salt, you will not replace your lost salt and can suffer high blood pressure. On the other hand, if you do not exercise, you do not lose much salt through your sweat and extra salt you eat can raises blood pressure.
There are only five long-term follow-up studies of salt intake and heart attacks. Two suggest that a low salt intake is harmful. Three other studies report that a high intake of salt is associated with strokes or heart attacks. Most data show that salt restriction lowers blood pressure in some people with high blood pressure, but most people with high blood pressure do not have their blood pressures lowered by going on a low-salt diet.
Most doctors who feel that a low-salt diet lowers blood pressure base their argument of the famous INTERSALT project, published in 1988. It showed that populations that have very high salt levels in their urines also had a high incidence of high blood pressure. The reason there is so much controversy about salt is that the data associating a high salt intake with high blood pressure applies only to people who do not exercise regularly.
Exercisers are harmed by significant salt restriction, while some non-exercisers appear to be harmed by taking in too much salt. Dr. James Gamble spent World War II studying the needs of American soldiers in the Pacific. His recommendation is that the only mineral that athletes and soldiers need in large amounts is sodium, known as table salt. The Gamble lectures on this topic were presented to Harvard Medical students right up to the time of his retirement in the 1960s. There is a huge data showing that severe salt restriction causes high blood pressure.
When you don't get enough salt, your adrenal glands put out huge amounts of aldosterone that constricts arteries and raises blood pressure and your kidneys put out huge amounts of renin that also contracts arteries and raises blood pressure. So, if you do not exercise, you do not sweat very much and you do not need very much salt. Too much salt increases blood volume which raises blood pressure. On the other hand, if you exercise vigorously, you sweat tremendously and lose a lot of salt and low salt levels raise blood levels of aldosterone and renin which causes high blood pressure. Furthermore, without the extra salt that you need, you will not recover from your hard bouts of exercise and you will be more likely to get injured or tired all the time.
The epidemiology of salt and hypertension. Clinical Autonomic Research, 2002, Vol 12, Iss 5, pp 353-357. DG Beevers. Beevers DG, City Hosp, Dept Med, Birmingham B18 7QH, W Midlands, ENGLAND
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