[img_inline align=”right” src=”http://padnws01.mcmaster.ca/images/martinodonnell” caption=”Dr. Martin O’Donnell, an associate clinical professor of medicine, and Dr. Salim Yusuf, a professor of medicine and executive director of the PHRI, have found that moderate salt intake was associated with the lowest risk of cardiovascular events, while a higher intake of sodium was associated with an increased risk of stroke, heart attack and other cardiovascular events and a low intake was associated with an increased risk of cardiovascular death and hospitalization for congestive heart failure. File photo.”]For years doctors have warned that too much salt is bad for your heart. Now a new
McMaster University study suggests that both high and low levels of salt intake may put
people with heart disease or diabetes at increased risk of cardiovascular complications.

The study, published in the Journal of the American Medical Association (JAMA) today,
found that moderate salt intake was associated with the lowest risk of cardiovascular
events, while a higher intake of sodium was associated with an increased risk of stroke,
heart attack and other cardiovascular events and a low intake was associated with an
increased risk of cardiovascular death and hospitalization for congestive heart failure.

The research, conducted by investigators in the Michael G. DeGroote School of Medicine
at McMaster University and the Population Health Research Institute (PHRI) at McMaster
and Hamilton Health Sciences, was co-led by Dr. Martin O'Donnell, an associate clinical
professor of medicine, and Dr. Salim Yusuf, a professor of medicine and executive
director of the PHRI.

“This research addresses an important population health issue – the association
between salt intake and cardiovascular disease,” said O'Donnell, who is also appointed
at the Health Research Board Clinical Research Facility, National University of Ireland, Galway.

“In general, previous observational studies have either reported a positive association,
no association or an inverse association between sodium intake and heart disease and
stroke. This has resulted in a lot of controversy. Our study is the first to report a J-
shaped association between sodium intake and cardiovascular disease, which may
explain why previous studies have found different results.”

For the McMaster observational study, the researchers examined 28,880 people at
increased risk of heart disease from clinical trials conducted between 2001 and 2008.
The researchers estimated 24-hour urinary sodium and potassium excretion from a
morning fasting urine sample.

Follow-up found more than 4,500 cardiovascular events occurred, making this one of
the largest studies examining the relationship between sodium excretion (a surrogate
measure of sodium consumption), as well as potassium excretion and cardiovascular
events.

Extensive and careful statistical analytic methods were used to determine the
association of urinary sodium and potassium with cardiovascular events, in particular
heart attack, stroke, hospitalization for congestive heart failure and death.

Compared with moderate sodium excretion (between 4 to 5.99 grams per day), the
researchers found that sodium excretion of greater than seven grams per day was
associated with an increased risk of all cardiovascular events, and sodium excretion of
less than three grams per day was associated with an increased risk of cardiovascular
death and hospitalization for congestive heart failure.

The findings call into question current guidelines for salt intake, which recommend less
than 2.3 grams (or 2,300 mg) per day. The guidelines are mostly based on previous
clinical trials that found blood pressure is lowered modestly when sodium intake is
reduced to this level (which was also found in the present study). However, there are no
large studies looking at whether such low levels of sodium intake reduce the incidence
of heart attacks and stroke.

Clarifying the optimal daily intake of sodium is particularly important in patients with
established heart disease, as they may be especially vulnerable to the cardiovascular
effects of very high- and low-salt intake and are most likely to receive
recommendations on restricting sodium in their diets, the authors concluded.

“Our study confirms the association between high-sodium intake and cardiovascular
disease. Our findings highlight the importance of reducing salt intake in those
consuming high-salt diets and the need for reducing sodium content in manufactured
foods that are high in salt,” said Yusuf, who is also vice-president of research, Hamilton
Health Sciences.

“However, for those with moderate (average) intake, whether further reduction of salt in
the diet will be beneficial is an open question. We believe that large clinical trials are the
most reliable way to determine if reducing sodium intake to lower levels is of benefit.”