Drinking at least one sugar-sweetened soft drink or fruit punch daily nearly doubles the risk of diabetes, according to the first large study to examine the suggested link.
Women who drank less than one of the beverages a month had half the risk of developing diabetes than those who drank one a day, according to the study of 91,000 nurses. The results were published in The Journal of the American Medical Association.
Women who increased the amount of sugar-sweetened drinks they consumed from one or less a week to one or more daily also were most likely to gain weight, picking up 17 pounds in eight years. The study provides more grist for a long-standing debate among nutritionists, government panels and the food and beverage industry about whether added sugars contribute to obesity and chronic diet-related diseases.
The American Beverage Association (ABA), formerly the National Soft Drink Association, criticized the study's focus on a single food as a cause of diabetes, saying many factors contribute to the disease.
"Soft drinks are a good subject to attack right now," said Richard Adamson, the beverage group's vice president for scientific and technical affairs.
The research is part of a long-running Harvard University-based study of diet, health and disease in 300,000 people. The research has produced influential findings on the dangers of trans-fatty acids and on the links between obesity and chronic disease and between consumption of red meat and colon cancer.
The latest study adjusted for potential risk factors for diabetes, such as physical activity, family history and body mass index, a measure of whether someone is overweight.
During the research period, there were 741 new cases of diabetes among the nurses, who ranged in age from the 20s to the 40s.
An editorial accompanying the study endorsed its conclusions.
The study "provides strong, scientifically sound evidence that excess calories from soft drinks are directly contributing to the epidemics of obesity and type 2 diabetes, at least in the U.S., and should help convince the U.S. government that further changes in health policy are needed," wrote Dr. Caroline M. Apovian, a physician and director of the Nutrition and Weight Management Center at Boston Medical Center.
The National Institutes of Health funded the study, which was conducted by researchers with the Harvard School of Public Health, Brigham and Women's Hospital and Boston Children's Hospital.
Lobbyists for beverage manufacturers assailed the study's conclusions. A spokeswoman for Coca-Cola referred questions to the American Beverage Association.
"The conclusions are scientifically unsound," said Adamson. "It's a totally unhealthy lifestyle that increased the risk. These women smoked more; they ate more; they had less protein intake; they had less cereal fiber intake; they exercised less. Give me a break, no wonder they had increased risk of type 2 diabetes."
The American Diabetes Association does not single out any food or beverage as causing the disease, said Dr. Nathaniel Clark, a physician who is the group's national vice president for clinical affairs. He said he believes extra pounds, rather than high sugar consumption, triggered diabetes in the women but added, "It is true (researchers) could not account for the increase in diabetes solely on weight gain."
The extra pounds accounted for only half the increased risk of diabetes, said Dr. JoAnn E. Manson, chief of preventive medicine at Brigham and Women's Hospital and one of the study's authors.
Researchers theorized that the risk of diabetes may increase because the sugars in sweetened drinks are rapidly absorbed in the body, raising blood sugar levels quickly and eventually leading to insulin resistance.
Consumers already have started to move away from sweetened soft drinks and toward diet sodas and bottled water. The sales volume of Coke Classic shrank 3% last year and Pepsi-Cola was down 4.5%.
The American Academy of Pediatrics recommended this year that schools eliminate sales of sweetened drinks. Some school districts have moved to restrict sales.
The study's authors called for public health strategies that would decrease consumption of sugar-sweetened beverages. Manson said that in the last 20 years, soft drink consumption has increased more than 60% in adults and has more than doubled in children.
"These trends do parallel the increased epidemic of obesity and type 2 diabetes, in both children and adults," she said. "There is an association."
The study also looked for a link between diet soda and diabetes, because of the caramel coloring that is in both diet and sugar-sweetened beverages. It found a "slight, nonsignificant" increased risk.
The study did not find a link between fruit juice and diabetes. Researchers said that could be because the naturally occurring sugars in fruit juice affect the body differently than the added sugars in sweetened drinks, or because the nutrients, fiber and plant chemicals in fruit juices may counteract the effects of sugar.
Sweetened soft drinks are the largest single food source of calories for Americans, contributing 7% of total calories consumed, according to the accompanying editorial in the medical journal.
To meet federal nutritional guidelines, the U.S. Department of Agriculture says Americans would need to cut in half their consumption of added sugars, found in products like sweetened drinks and many processed foods.
Both Coke and Pepsi have introduced lower-sugar colas this year, but consumer response to C2 and Pepsi Edge has been modest, analysts say.
The medical journal's editorial calls for the government to redefine guidelines for sugar consumption, especially in soft drinks, and to support efforts to remove soda machines from schools or replace the products with healthier options.
An independent scientific panel studying federal nutrition guidelines disagreed this summer on the role of sugar on weight gain or body mass index but concluded that individuals who consumed foods or beverages high in added sugar took in more calories than those who consumed low amounts of added sugar. They also noted that it is more difficult to regulate calories in sugar-sweetened drinks than in solid food.
The ABA had its own opinions on the matter, noting it is scientifically indefensible to blame any one food or beverage for increasing the risk of type 2 diabetes, a disease which is commonly known to have multiple causes and risk factors.
The association further states that the study “irresponsibly proposes an association between sugar-sweetened soft drink consumption and type 2 diabetes in women. This interpretation of the results reflects neither reality nor even this study's own results. In addition to soft drinks, this study found significant correlations between low cereal fiber intake, low protein intake, low magnesium intake, smoking, low physical activity, increased total caloric consumption and type 2 diabetes.”
"It is inexplicable that the authors have chosen to focus solely on sugar-sweetened beverages in this way," said Adamson. "Neither soft drinks nor fruit juice consumption nor sugar intake are listed by the National Institutes of Health, the American Diabetes Association or the majority of published medical literature as risk factors for type 2 diabetes. This study provides no evidence to support the inflammatory allegation that sugar-sweetened beverages are a cause of type 2 diabetes."
"A careful reading of the paper reveals that it was an unhealthy lifestyle, not consumption of a particular food or beverage, that increased the women's risk for type 2 diabetes. In addition to the statistical findings of this study being weak, the study also did not adjust for all known diabetic risk factors," Adamson said.
Sugar intake and a higher Body Mass Index (BMI) are not directly linked, commented the ABA. As recently summarized by the Institute of Medicine (IOM), studies have not shown a direct link between increased sugar intake and increased obesity rates. The IOM report also states that the effects of increased intake of total sugar or energy are not consistent and that "there is no clear and consistent association between increased intake of added sugars and BMI."
Epidemiological evidence from other studies also indicates that sugar consumption is not an independent risk factor for type 2 diabetes. A recent literature review by Rob van Dam (European Journal of Epidemiology 2003;18:1115-1125) notes, "Contrary to popular belief, data do not suggest that a higher proportion of sucrose in the diet increases risk for type 2 diabetes independent of body fatness."
It should also be noted that in the Nurses' Health Study I, it was concluded that sucrose intake was not related to risk of type 2 diabetes (Colditz et al., American Journal of Clinical Nutrition 1992;55:1018-1023). This previous finding was ignored in the Schulze study, which has many of the same authors.
In the current study, the ABA continues, the correlations between increased sugared soft drink intake and type 2 diabetes did not differ significantly from those between diet soft drinks and type 2 diabetes. There is no reasonable scientific basis for any association between diet soft drink consumption and either weight gain or obesity. The lack of difference between regular and diet soft drinks brings into question the validity of the analytical methods used in the current report, attests the ABA.
In a key paragraph of the comment section, the authors note that errors in dietary assessment can solely account for a lack of association. However, dietary self-assessment tools are known to produce errors of omission and errors in both underestimation and overestimation of quantities consumed. Dietary self-assessment can result in bias errors both in failing to find associations that do exist and in falsely finding associations that do not exist. Because in this study consumption of sugar-sweetened beverages was associated with several demonstrated diabetes risk factors (e.g., cigarette smoking, low physical activity, low cereal fiber consumption and low magnesium intake), it is impossible to determine which of these variables was most important as a factor linked with incidence of diabetes.
Epidemiological studies often have these types of issues (Smith and Ebrahim, British Medical Journal 2002;325:1437-1438), but in this study, the authors chose to ignore many of the factors found to be linked to diabetes incidence and instead focus solely on a link with increased sweetened beverage intake. In addition, no association with weight gain or type 2 diabetes was found in those women who regularly consumed soft drinks throughout the study. The only association was found between weight gain or type 2 diabetes and women who dramatically increased their soft drink intake during the study. This lack of correlation between disease and constant soft drink intake suggests that soft drinks were not the most important factor, the ABA believes: “The narrow focus on soft drinks in light of many associated factors is faulty science. It is the total unhealthy lifestyle of the subjects, not a single factor, that seemed to lead to greater risk for overweight and type 2 diabetes.”
To maintain a healthy lifestyle, it is important to consume a variety of foods and beverages in moderation and to get daily exercise, cautions the ABA. Soft drink companies offer consumers a variety of beverages, including bottled water, teas, sports drinks, fruit juices, fruit drinks, regular soft drinks, mid-calorie soft drinks and diet drinks.
"Soft drink companies have provided more consumer choice by expanding their no-calorie and low-calorie options dramatically and introducing new, smaller packaging options, including eight-ounce cans and 13.2- and 14-ounce plastic bottles, to help consumers manage their caloric intake," said Kathleen Dezio, a spokeswoman for the ABA.