A team of Canadian scientists is hunting for the salt gene, hoping to unlock the mystery of why some ethnic groups are highly sensitive to salt and suffer from abnormally high rates of hypertension.
Blacks and South Asians are three times more likely than Caucasians to suffer from high blood pressure, a condition that is the leading cause of heart disease and stroke. Only cancer kills more Canadians every year.
The link between ethnicity and high blood pressure is well known, but until now, researchers have been unable to pinpoint the cause. Now, researchers at the University of Ottawa’s Heart Institute have launched an ambitious, multi-million-dollar, three-year study to uncover the genetic determinations of salt sensitivity. Their success could revolutionize the treatment and prevention of hypertension, which affects 20 per cent of Canadians, at an annual cost of $430-million.
Adding to the complexity, there is variation within these populations: some blacks and South Asians are not at all salt sensitive, and some Caucasians conserve salt.
Researchers at the University of Ottawa’s Heart Institute have launched an ambitious, multi-million-dollar three-year study to uncover the genetic determinations of salt sensitivity. This could revolutionize the treatment and prevention of hypertension, which affects 20 per cent of Canadians, at an annual cost of $430-million.
“Blacks are more susceptible to high blood pressure and to being salt sensitive than Caucasians. But looking at someone’s skin colour doesn’t tell you this, because some are not at risk at all, and vice versa for Caucasians,” said Frans Leenen, a cardiologist and director of the Heart Institute’s hypertension unit. “This is the first study in the world which will look at the genome sequence, and salt sensitivity.”
Dr. Leenen, the principal investigator, predicts there is not one, but 10 to 12 salt genes. Mapping them will pave the way for a salt sensitivity diagnostic test.
Salt sensitivity means people retain salt and water in their blood vessels, making the vessels more rigid and constricted. The heart then has to work harder to pump blood through the vessels, causing an elevation in blood pressure. Genetic variants play a role in determining how much blood vessels constrict.
If people knew they were salt-sensitive, they would know whether reducing dietary sodium would bring down their blood pressure.
The average Canadian takes in about 3,100 milligrams of sodium a day – more than double the recommended intake and significantly more than the upper limit most people can consume without compromising their health.
There are many environmental causes of high blood pressure, as well as genetic. But doctors say that by reducing dietary sodium, one fifth of the five million cases of hypertension in Canada could be eliminated.
Ethnic differences in hypertension rates have been well documented for many years in the United States. But in Canada, this health issue wasn’t studied until last year when the Heart and Stroke Foundation of Ontario commissioned a survey that found blacks and South Asians (Indians, Bangladeshis and Pakistanis) are three times more likely to have high blood pressure compared with the general population. They are also likely to develop it at a younger age.
One third of blacks and South Asians have high blood pressure, compared with about 21 per cent of the general population, and about 19 per cent of East Asians (Chinese, Japanese, Koreans).
The elderly, diabetics and people who are obese or have kidney disease are also salt sensitive.
“Knowing the hypertension rates are on the rise due to an aging and diverse population is an important wake-up call,” said Sheldon Tobe, a nephrologist and spokesman for the Heart and Stroke Foundation.
The elderly, diabetics and people who are obese or have kidney disease are also salt sensitive.
