Looking at the big picture

A Memorial University researcher studies the short- and long-term impacts of dietary sodium

[ Back to main article ]

Kids don't think twice about salt in their food. Most adults don't, either. In fact, it's only when our doctors tell us that it's time to put down the salt shaker that we really start to pay attention to the sodium content of the food we eat. According to Dr. Bruce Van Vliet, a researcher at Memorial University of Newfoundland, it may be too late at that point.

"When we think about how salt affects blood pressure, we tend to think of it as a simple event: if you eat salt, your blood pressure will probably go up; if you restrict salt, your blood pressure will probably go down," says Dr. Van Vliet. "But this is an oversimplification. We need to think about it in a more sophisticated way."

Dr. Van Vliet is a scientist who wants to understand the "big picture" of sodium's impact on blood pressure. During his post-doctoral research, he studied mathematical models of how sodium consumption affects blood pressure over time. His recent research and modeling reveals that sodium has different effects on our health in the short- and long-term, and this is an important message for salt-lovers.

When someone goes on a high-salt diet for a few days, his or her blood pressure will often increase in response. This short-term response is easily measured, and can usually be reversed by reducing salt intake.

"So if we took a group of people who were hypertensive and put them on a low-salt diet and their blood pressure came down, we'd say, 'Oh, you're salt-sensitive!'. And that's a great concept," says Dr. Van Vliet. "But in addition to that, there's a whole other effect of salt on blood pressure."

In societies where sodium consumption is high, such as North America, blood pressure rises as a person ages. This is a slower phenomenon that isn't necessarily reversible with medication or dietary changes.

"The more sodium the society eats, the more the blood pressure rises with age," explains Dr. Van Vliet. "And when I say with age, I mean over decades. You can't see it in an individual very easily, so it's hard to investigate. But what we can do is look at it in animals."

And there is a growing body of evidence that this long-term impact may begin very young, perhaps before birth. Dr. Van Vliet is beginning to investigate just how early sodium intake begins to cause long-term hypertension.

"There are a growing number of studies which show that the earlier in life you are exposed to salt, the more profound the effect will be," says Dr. Van Vliet.

This is raising the question of whether salt consumed by a young mother when she is breastfeeding, or even pregnant, could increase her child's risk of hypertension later in life. Dr. Van Vliet's findings could eventually lead to changes in the dietary recommendations for pregnant women.

"The maternal nutritional environment during pregnancy seems to alter the offspring in a long-term way. It can't change the offspring's genetic code, but it can change the manner in which the offspring's genes are used," explains Dr. Van Vliet. "We want to find out if the sodium a mother consumes during her pregnancy can have this kind of reprogramming influence on her baby's genes."

The Study

With the help of funding from the Canadian Institutes of Health Research, Dr. Van Vliet and his colleagues performed experiments in salt-sensitive rats, known as Dahl rats, to illustrate that salt-induced hypertension can occur in short- and long-term phases, with varying levels of reversibility.

Next, he plans to look at the impact of high-salt diets on pregnant mice and their offspring. This research could help reveal whether or not the sodium a mother eats during her pregnancy affects her offspring's blood pressure later in life.