Glycemic Index Linked to Increased Risk of Major Cardiovascular Events, Mortality

David Jenkins, MD, PhD

A global analysis of dietary information suggests diets high in poor quality carbohydrates was linked to a greater risk of heart attack, stroke, and death.

An analysis that included more than 135,000 participants from 5 continents suggests a diet with a high glycemic index was associated with a 21% increase in risk of a major cardiovascular event or death among those with no history of cardiovascular disease and this risk became greater among those with preexisting cardiovascular disease.

“I have been studying the impact of high glycemic diets for many decades, and this study ratifies that the consumption of high amounts of poor quality carbohydrates is an issue worldwide," said lead investigator David Jenkins, MD, PhD, professor of nutritional sciences and medicine at the University of Toronto's Temerty Faculty of Medicine and a scientist in the Li Ka Shing Knowledge Institute of St. Michael's Hospital, Unity Health Toronto, in a statement.

While many studies have explored diet and nutrition and their association with cardiovascular risk, investigators pointed out most of these studies had examined associations in high-income western nations. To determine whether results seen in these studies were similar in other parts of the world, investigators designed the current study as an analysis of data from within the Prospective Urban and Rural Epidemiology (PURE) study.

From the PURE study, investigators obtained data related to a cohort of 137,851 participants between the ages of 35-70 years from 20 countries on 5 continents. Of note, this cohort had a median follow-up of 9.5 years and data from country-specific food-frequency questionnaires. In total, food questionnaires examined consumption of 3200 food items.

Investigators used this information to calculate hazard ratios using Multivariable Cox frailty models. The primary outcome of the analyses was a composite of major cardiovascular events or death from any cause. Investigators included cardiovascular death, nonfatal myocardial infarction, stroke, and heart failure in the composite outcome.

For the purpose of analysis, investigators created 5 quintiles to compare glycemic index among patients. In fully adjusted analyses, investigators included urban or rural location, country

income category, education level, smoking status, physical activity, waist-to-hip ratio, history of diabetes, statin use, use of blood-pressure medication, total daily energy intake, consumption of dietary fiber, and consumption of whole-grain cereals as variables.

During follow-up, 8780 deaths and 8252 major cardiovascular events occurred within the study cohort. After adjustment for confounding factors, results indicate those with a high glycemic index were at an increased risk of a major cardiovascular event or death. Investigators pointed out this apparent increase in risk was present among those with preexisting cardiovascular disease (HR, 1.51; 95% CI, 1.25-1.82) and among those without preexisting cardiovascular disease (HR, 1.21; 95% CI, 1.11-1.34). Investigators noted similar associations were seen when examining individual aspects of the composite endpoint.

"PURE study papers have already indicated that not all carbohydrates foods are the same. Diets high in poor quality carbohydrates are associated with reduced longevity, while diets rich in high quality carbohydrates such as fruit, vegetables and legumes have beneficial effects," Jenkins said.

This study, “Glycemic Index, Glycemic Load, and Cardiovascular Disease and Mortality,” was published in the New England Journal of Medicine.