Research on the Impact of a Sodium (Salt) Diet

Eat less salt to reduce risk of stroke
By: Frank Drea
The Toronto Telegram, Wednesday, September 15, 1971

Salt, still virtually sacred in many parts of the world and once considered essential to ward off the impact of intense heat on the body, is gaining a new image - as an extremely dangerous part of the diet once you reach middle age.

Forty years ago, Dr. W. W. Priddle, who pioneered the study of geriatrics, the problems of aging, in Ontario and who heads the Government's advisory committee on geriatrics, was recommending that high-blood pressure patients keep their salt (sodium) intake to a minimum.

Since 1931, his research into hypertension has indicated that too much sodium can be exceedingly hazardous to those with a tendency toward high blood pressure. For the control of hypertension is regarded as the key to the prevention - or at least the repetition - of strokes.

The impact of the stroke on society is enormous. The Ontario Geriatric Study Centre has found that almost two thirds of incapacities among older people are from complications of hypertension and degenerative cardiovascular diseases. Prevention of the personal tragedy that afflicts victims of strokes and easing of high economic costs of caring for them have become major goals of geriatric work.

"More and more evidence is accumulating that the most important factor in strokes is high blood pressure," says Dr. Priddle, winner of the Malford W. Thewlis Award of the American Geriatric Society in 1970. "There are four times as many strokes among people with high blood pressure compared to those with normal blood pressure."

But while his work in the field of hypertension has yielded growing evidence that high sodium intake must be controlled in the prevention of strokes, modern living has introduced enormous amounts of salt into daily meals.

Where salt was once a preservative, it is now hidden flavouring, especially in canned foods. Canning processes eliminate many mineral elements from vegetables, fruits and cereals so, to put taste into the food, a considerable amount of sodium chloride is added.

"Controlling salt intake is much more than just refusing to pour table salt on your food," says Dr. Priddle. "Convenience foods, canned foods, meats, bacon and sausages contain tremendous amounts of salt when placed on the table. Tests have shown that even babies can consume enormous amounts of salt without any being added to their food."

He feels the presence of so much sodium chloride in food has conditioned us to desire salt. But if present trends in evidence continue, the conventional foods of today may be replaced by "salt free" processing.

Dr. Priddle recommends people eat as much fresh food as possible and even if they are not subject to high blood pressure they should start acquiring a taste for "salt free" processed foods.

What about the practice in heavy industry and construction to issue salt tablets to workers when they are subject to intense heat?

Dr. Priddle said he had never seen a low salt diet affect a patient in intense heat. He doesn't think salt tablets have any beneficial effect.

The importance of diet, particularly the sodium-potassium balance, has been one of the results of research by the Geriatric Study Centre into strokes and the rehabilitation of stroke victims.

In a publication in 1962, Dr. Priddle and his associates called for the treatment of hypertension in the early stages as well as in the elderly on a prophylactic basis. They had shown that it could be accomplished with a considerable degree of safety.

A 1968 report compiled by the cardiovascular unit of the Geriatric Study Centre showed this result from a four year controlled study of residents of homes for the aged:

"Treatment with no added salt diet, small does of chlorothiazide and potassium supplement, reduced the mortality rate by 50 percent. This encourages us to continue to treat hypertension in the elderly on a prophylactic basis."

The study involved men and women between 75 and 89 years of age. Dr. Priddle says there were fewer strokes than expected and credits the low amount of sodium in their diet.

"Prevention of the stroke is important not only because of the comfort of the individual and personal happiness, there is the economic consideration to society," he said. "It is becoming more and more costly to provide care for the stroke victim, particularly with the longer span of life."

There is also the problem of "little strokes," relatively mild ones that do not paralyze but steadily wear down a person by impairing more and more faculties.

Dr. Robert Laird, who was chief surgeon at Toronto Western Hospital and helped start a medical school in Nigeria, feels that treatment of the stroke has advanced greatly. Where hospital was once the beginning and end of the treatment, now it is just the beginning.

He also feels that research has helped erase the "stigma" of the stroke. For it had been associated with senility and old age and few victims who were restored to health would admit they had suffered a stroke.

Modern medicine has also brought new research into the after-care of the stroke victim. Antibiotics have eliminated many of the fatal complications such as pneumonia and septic infections that often followed a stroke.

But while therapy, the activation and rehabilitation of the stroke victim are important, the prevention of the stroke is the goal. This is the reason for the intense interest in high blood pressure.

Cerebral thrombosis is the most common vascular cause of strokes. Professionally, it is referred to as atherothrombotic brain infraction (ABI). A lengthy study in Framingham, Mass., where more than 5,200 men and women between 30 and 62 years had their blood pressure recorded over 14 years, reported an extremely close relationship between high blood pressure and ABI.

The study also showed that control of any kind of hypertension was they key to the prevention of the stroke. This is why the first project of the Ontario Geriatric Association was to help sponsor the study centre's research into high blood pressure.

Most noteworthy has been the analysis of the urine of people before and after they went on salt free diets.

The analysis also showed the effectiveness of drugs in clearing the residue of sodium from blood vessels. For the human organism preserves sodium, increasing the chances of high blood pressure triggering a stroke.

Significantly, almost 75 years ago, vegetarian movements in England were urging the public to give up salting their foods. Just as significantly, one of their tracts conceded that going without salt was difficult and one had to learn to like food that had not been salted.

In those 75 years the stroke has advanced to become the third greatest cause of death, a major disabler and an extremely costly disability because the victim of a severe stroke will need care as long as he lives.