A diet high in sodium increases the risk of heart disease-related mortality in overweight individuals, according to a study published in the December 1 issue of the Journal of the American Medical Association (JAMA).
The study, which was funded by the National Heart, Lung, and Blood Institute (NHLBI), followed the health of a representative group of U.S. adults over a 20-year period. Among those adults who were overweight, there was a 63% greater risk of death from cardiovascular disease for those who consumed the highest amounts of sodium relative to their caloric intakes compared to adults who consumed the lowest amounts of dietary sodium.
"This new and compelling evidence couples dietary sodium intake with an increased risk of death from coronary heart disease. This relationship is compounded by overweight, which, as we know has become a serious problem in this country," said NHLBI Director Dr. Claude Lenfant.
The new analysis is based on data from participants in the First National Health and Nutrition Examination Survey (NHANES I) who were recontacted several times over 20 years in the NHANES I Epidemiologic Follow-up Study (NHEFS); both studies were conducted by the National Center for Health Statistics (NCHS). This analysis included 9,485 of the original 14,407 adult participants in NHANES I (1971-1975). From 1971 to 1992, there were 810 total deaths among the 2,688 overweight participants, with 214 of these deaths from heart disease.
The study, led by Dr. Jiang He of the Tulane University School of Public Health and Tropical Medicine in New Orleans, also evaluated the relative risk of disease and death from cardiovascular factors associated with a 100 mmol/day increase in sodium intake, about 6 grams or 1 1/4 teaspoons of salt. The analysis showed that among overweight adults cardiovascular mortality risk increased 61% for each additional 100 mmol of dietary sodium consumed on a daily basis.
Additionally, the study showed an 89% increase in the risk of stroke death from each additional 100 mmol of sodium consumed per day among overweight adults.
Overweight individuals, as they consume more calories, also consume more sodium, and have been shown to absorb and retain sodium differently from non-overweight people. An estimated 97 million adults in the United States are overweight or obese.
NHLBI published, in 1998, in cooperation with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) Clinical Guidelines on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults. The clinical guidelines define overweight as a body mass index (BMI) of 25-29.9 and obesity as a BMI of 30 and above.
"Overweight is a common and important cardiovascular disease risk factor. This is particularly troubling, as the prevalence of obesity has increased progressively during recent decades among all racial and ethnic groups in the U.S. To reduce the risks of cardiovascular disease, both weight loss and sodium reduction should be recommended. And evidence from a variety of sources indicates that for people who are not overweight, moderation in sodium intake is the wisest course," said Paul Whelton, MD, investigator on the study and Senior Vice President for the Health Sciences at Tulane University.
The NHLBI continues to support the sodium and salt intake statement recommended by the National High Blood Pressure Education Program. A comprehensive review of the evidence suggests that, as part of an overall healthy diet, Americans should consume no more than 2,400 mg of sodium a day, an amount which is just above the 100 mmol increase used in the current study. This amount is also recommended in the 1995 Dietary Guidelines for Americans, published by the U.S. Department of Health and Human Services, and in the 1996 Dietary Guidelines for Healthy American Adults, recommended by the American Heart Association.
Catherine Loria, PhD, an NHLBI epidemiologist and a co-investigator on the study is available for interviews. To arrange an interview with her, call the NHLBI Communications Office at 301-496-4236.