LOS ANGELES – People who consume an excessive amount of sodium each day or drink diet soda daily have a significantly increased risk for stroke or other vascular events, according to two separate analyses of participants in the prospective, observational Northern Manhattan Study.
Consumption of greater than 4,000 mg of sodium daily, when compared with the American Heart Association’s new recommendation of 1,500 mg/day, was associated with a nearly threefold higher risk of stroke. This increased risk occurred independently of the confounding effects of hypertension.
A separate analysis of diet soda intake among many of the same individuals also found that having at least one diet soda each day was associated with nearly a 50% increase in the risk of stroke, myocardial infarction, or vascular death, compared with people who did not drink soda at all.
The Northern Manhattan Study began in 1993 and enrolled 3,298 area residents by 2001. These individuals have been followed for up to 10 years. The subsets of individuals from the study that were included in each analysis were very similar: Their mean age was 69 years and 36% were male. The multiethnic makeup represented the northern Manhattan area, comprising approximately 53% Hispanics, 23%-24% blacks, 20%-21% whites, and 2%-4% other ethnic groups.
At baseline, all of the subjects underwent a battery of tests, including sociodemographics; a vascular risk profile; blood pressure; anthropometric measurements; fasting blood sugar; and a neurologic exam. They also completed the National Cancer Institute Food Frequency Questionnaire, which was modified to reflect Hispanic dietary patterns.
"Most of our study population [88%] consumed more than the American Heart Association’s 1,500 mg/day recommendation" for sodium intake, Hannah Gardener, Sc.D., said at the conference. "More importantly, 21% consumed more than 4,000 mg of sodium per day and, at this level, there was an increased stroke risk of more than 2.5-fold, independent of baseline hypertension, and across all the ethnic groups in the study."
The AHA recommendation was issued in January. An AHA science advisory board said that the 1,500-mg daily limit would promote optimal cardiovascular health. However, it’s much less than the U.S. Dietary Guidelines, which call for a daily intake of no more than 2,300 mg – about a teaspoonful of salt.
Dr. Gardener and her colleagues’ analysis of sodium intake and stroke risk included 2,657 participants who had full dietary and sodium intake information available and had not experienced a prior heart attack or stroke.
The participants’ mean daily sodium intake was 3,031 mg (median was 2,787 mg). "Only 12% of the cohort adhered to the AHA recommendation of less than 1,500 mg/day, and 44% consumed more than 3,000 mg/day," said Dr. Gardener, an epidemiologist at the University of Miami. Nearly one-fourth of the group (21%) consumed 4,000 mg or more of sodium each day.
During a mean 10-year follow-up period, 227 strokes occurred. A multivariate analysis found that the risk of stroke steadily increased with increases in sodium intake, although the difference in intake did not achieve statistical significance until intake reached 4,000 mg/day or more. At that level, subjects had nearly three times greater risk for stroke than did those who kept to the 1,500 mg/day recommendation (risk ratio 2.67). This analysis was adjusted for demographics and behavioral risk factors (education, alcohol, smoking, physical activity, and daily caloric intake), as well as vascular disease risk factors (diabetes, hyperlipidemia, hypertension, body mass index, and prior cardiac disease).
When salt intake was treated as a continuous variable, each 500-mg increase above 1,500 mg corresponded to an 18% increase in risk for stroke.
Because the risk was so dramatically elevated in the highest intake group, Dr. Gardener voiced support for the revised sodium intake recommendation. "Our results suggest that the new AHA strategic dietary goal will help promote cardiovascular and brain health and can be used to target dietary behavior as a method of modifying disease risk."
In the other analysis, Dr. Gardener reported that study participants who reported drinking diet soda every day had 48% greater risk for stroke or heart attack than did non–soda drinkers. This association was adjusted for cardiovascular risk factors, including smoking, physical activity, alcohol and caloric intake, metabolic syndrome, peripheral vascular disease, and prior cardiac disease.
This analysis included 2,564 individuals who provided information about soda intake and who had not experienced a previous heart attack.
The investigators divided the cohort into seven categories based on soda consumption. These included no diet or regular soda (less than one per month, 35%), occasional regular soda (from one per month to six per week, 30%), daily regular soda (seven or more per week, 11%), occasional diet soda (8%), daily diet soda (5%), occasional diet plus any regular soda (9%), and daily diet plus any regular soda (2%).