The Journal of the American Medical Association

August 25, 2004 Vol. 292 No. 8

Sugar-Sweetened Beverages, Weight Gain, and Incidence of Type 2 Diabetes in Young and Middle-Aged Women

Matthias B. Schulze, DrPH; JoAnn E. Manson, MD; David S. Ludwig, MD; Graham A. Colditz, MD; Meir J. Stampfer, MD; Walter C. Willett, MD; Frank B. Hu, MD

ABSTRACT

Context Sugar-sweetened beverages like soft drinks and fruit punches contain large amounts of readily absorbable sugars and may contribute to weight fain and an increased risk of type 2 diabetes, but these relationships have been minimally addressed in adults.

Objective To examine the association between consumption of sugar-sweetened beverages and weight change and risk of type 2 diabetes in women.

Design, Setting, and Participants Prospective cohort analyses conducted from 1991 to 1999 among women in the Nurses’ Health Study II. The diabetes analysis included 91 249 women free of diabetes and other major chronic diseases at baseline in 1991. The weight change analysis included 51 603 women for whom complete dietary information and body weight were ascertained in 1991, 1995 and 1999. We identified 741 incident cases of confirmed type 2 diabetes during 716 300 person years of follow-up.

Main Outcome Measures Weight gain and incidence of type 2 diabetes.

Results Those with stable consumption patterns had no difference in weight gain, but weight gain over a 4 year period was highest among women who increased their sugar sweetened soft drink consumption from 1 or fewer drinks per week to 1 or more drinks per day (multivariate-adjusted means, 4.69 kg for 1991 to 1995 and 4.20 kg for 1995 to 1999) and was smallest among women who decreased their intake (1.34 ad 0.15 kg for the 2 periods respectively) after adjusting for lifestyle and dietary confounders . Increased consumption of fruit punch was also associated with greater weight gain compared with decreased consumption. After adjusting for potential confounders, women consuming 1 or more sugar-sweetened soft drinks per day had a relative risk [RR] of type 2 diabetes of 1.83 (95% confidence interval [CI], 1.42-2.36; P<.001 trend) compared with those who consumed less then 1 of these beverages per month. Similarly, consumption of fruit punch was associated with increased diabetes risk (RR for >1 drink per day compared with <1 drink per month, 2.00; 95% CI, 1.33-3.03; P = .001)

Conclusion Higher consumption of sugar-sweetened beverages is associated witha greater magnitude of weight gain and an increased risk for development of type 2 diabetes in women, possibly by providing excessive calories and large amounts of rapidly absorbable sugars.

INTRODUCTION

Type 2 diabetes mellitus affects about 17 million US individuals. The prevalence of diabetes has increased rapidly during the last decades in parallel to the obesity epidemic. Coinciding with the increasing prevalence of obesity and type 2 diabetes, soft drink consumption in the United States increased by 61% in adults from 1977 to 1997 and more than doubled in children and adolescents from 1977 - 1978 to 1994 - 1998. Recent evidence suggest an association between the intake of sugar-sweetened soft drinks and the risk of obesity in children, but data among adults are limited. Besides contributing to obesity, sugar-sweetened soft drinks might increase risk of diabetes because they contain large amounts of high-fructose corn syrup, which raises blood glucose similarly to sucrose. Soft drinks are the leading source of added sugars in the US diet, and each serving represents a considerable amount of glycemic load that may increase risk of diabetes. + + + Because the majority of sugar-sweetened beverages consumed in this cohort are soft drinks, we particularly emphasized soft drink consumption.

METHODS

Study Population

The Nurses’ Health Study II is a prospective cohort study of 116 671 female US nurses aged 24 to 44 years at study initiation in 1989. This cohort is followed up by using biennial mailed questionnaires, with a follow-up rate exceeding 90% for every 2-year period. For the analyses presented here, women are excluded if they did not complete a dietary questionnaire in 1991 or if more than 9 items on it were left blank; if the reported dietary intake was implausible with regard to total energy intake (ie, <500 kcal/d or >3500 kcal/d); if they had a history of diabetes, cancer (except nonmelanoma skin cancer), or cardiovascular disease at baseline; or if they had not provided data on physical activity in 1991. The final sample of the diabetes analysis consisted of 91 249 women. For the analysis in weight change, we also excluded women who did not complete the questions on sugar-sweetened soft drinks consumption, who had a history of diabetes or cardiovascular disease before 1995 or reported the diagnosis of cancer (except nonmelanoma skin cancer) on any questionnaire, who did not report body weight or any questionnaire, or who had no data on physical activity assessed in 1997. These exclusions left a total of 51 603 women for the analyses. The study was approved by the human research committees at the Harvard School of Public Health and Brigham and Women’s Hospital, Boston, Mass; completion of the self administered questionnaire was considered to imply informed consent.

Dietary Assessment

In 1991, the mailed questionnaire included a 133-item semiquantitative food frequency questionnaire. Women were asked how often thy had consumed a commonly used unit or portion size of each food on average over the previous year, including 3 items on consumption of sugar-sweetened soft drinks ("Coke, Pepsi, or other cola with sugar" "caffeine-free Coke, Pepsi, or other cola with sugar,"and "other carbonated beverages with sugar"), 4 items on fruit juice("apple juice," "orange juice," "grapefruit juice," and "other juice"), 1 item on fruit punch, and 3 items on diet soft drinks ("low-calorie cola with caffeine," "low-calorie caffeine free cola," and "other low-calorie beverages"). We summed the intake of single items to create a total of sugar sweetened soft drink, diet soft drink, and fruit juice consumption. The 9 possible responses, ranging from "never" to "6 or more times per day," were aggregated into 4 categories (<1 drink per month, 1-4 drinks per month, 2-6 drinks per month, and >1 drink per day). Similar questionnaires were used to collect dietary information in 1995 and 1999. Nutrient intakes were computed my multiplying the frequency response by the nutrient content of the specified portion sizes. Values for nutrients were derived from the US Department of Agriculture sources and supplemented with information from manufacturers. The validity and reliability of food frequency questionnaires similar to those used in the Nurses’ Health Study II have been described elsewhere. Briefly, the correlation coefficients between questionnaire and multiple dietary records were 0.84 for cola type soft drinks (sugar-sweetened and diet combined), 0.36 for other carbonated soft drinks, 0.84 for orange juice, and 0.56 for fruit punch in the Nurses’ Study I and ere 0.84 for sugar-sweetened cola, 0.55 for other sugar-sweetened soft drinks, and 0.73 for diet cola, 0.74 for other diet soft drinks, 0.78 for orange juice, 0.77 for apple juice, 0.75 for grapefruit juice, and 0.89 for other fruit juices in the Health Professionals Follow-up Study, 2 similar cohort studies among US health care professionals.

Assessment of Nondietary Exposures

Information on age, weight, smoking status, contraceptive use, postmenopausal therapy, ad pregnancies were collected in biennial questionnaires. We calculated body mass index (BMI) as weight in kilograms divided by the square of height in metres, height was assessed at baseline only. Self reports of body weight were highly correlated with technician measured weights(r = 0.96) in the Nurses’ Health Study I. Family history of diabetes was reported in 1989 only. In 1991 and 1997, participants were asked how many flights of stairs they climb daily and te amount of times per week they spent on average in each of the following activities: walking or hiking outdoors; jogging; running; bicycling; lap swimming; tennis; squash; or racquetball playing; calisthenics; and other aerobic recreation. From this information , weekly energy expenditure in metabolic equivalent hours were calculated, weighting each activity by its recorded intensity level. Physical activity reported on the questionnaire was highly correlated with activity recorded in diaries or by 24-hour recall (0.79 vs 0.62). Because physical activity was not assessed in 1995 or 1999, for our analysis on weight change, we used 1997 estimates for both of these time points instead.

Ascertainment of Type 2 Diabetes

Women reporting a new diagnosis of diabetes on any of the biennial questionnaires were sent supplementary questionnaires asking about diagnosis and treatment of their diabetes, as well as history of ketoacidosis to confirm the self report and to distinguish between type 1 and type 2 diabetes. In accordance with the criteria of the National Diabetes Data Group, confirmation of diabetes required.

Statistical Analysis

We calculated the mean weight changes for groups defined by change in soft drink consumption from 1991 to 1995 and from 1995 to 1999, adjusting for age, alcohol intake, physical activity, smoking, BMI, and other lifestyle and dietary confounders at baseline for each period. We also adjusted for food items that have been previously shown to be associated with sugar-sweetened soft drink consumption. We additionally adjusted for changes in the covariates (except BMI) during the period 1991 to 1995 in a separate model for that period.

RESULTS

Sugar-sweetened Beverages and Weight Change

Women with a higher intake of sugar-sweetened soft drinks tended to be less physically active, to smoke more, and to have higher intake of total energy and lower intake of protein, alcohol, magnesium, and cereal fiber. Intake of total carbohydrates, sucrose, and fructose as well as the overall glycemic index were higher in women with greater sugar-sweetened soft drink consumption, but starch intake was lower.

Women who increased their sugar-sweetened soft drink consumption between 1991 and 1995 from low to high also increased their reported total energy intake by 358kcal/d on average. In contrast, women who reduced their sugar-sweetened soft drink consumption between 1991 and 1995 also reduced their total energy consumption by 319 kcal/d on average. Changes in energy intake from food sources other than sugar-sweetened soft drink accounted for only 27% to 34% of these changes in total energy intake. Similar associations were observed for the period of 1995 - 1999.

For both periods 1991 to 1995 and 1995 to 1999, women who increased their consumption of sugar sweetened soft drinks from low to high had significantly larger increases in weight and BMI than women who maintained a low or a high intake or substantially reduced their intake. The lowest weight gain and increase in BMI were observed among women who reduced their intake from high to low. Because lifestyle and dietary changes might confound these association, we repeated the analysis for the period 1991 to 1995, additionally controlling for changes in physical activity and other covariates over time, but results remained similar. We repeated our analysis excluding all women who reported a pregnancy in 1991, 1995, or 1999, but this had minimal impact on our observations.

Women who increased their soft drink consumption from 1991 to 1995 and maintained a high level of intake during 1995 - 1999 gained, on average, 8.0 kg between 1991 and 1999, whereas women who decreased their consumption between 1991 and 1995 and maintained a low level o intake gained 2.8 kg between 1991 and 1999 on average.

Sugar-Sweetened Beverages and Risk of Diabetes

During 716 300 person-years of follow-up, we documented 741 new cases of type 2 diabetes. Greater sugar-sweetened soft drink consumption was strongly associated with progressively higher risk of type 2 diabetes. The age adjusted RR was 1.98% for women consuming 1 or more sugar-sweetened soft drinks per day compared with those consuming less than 1 sugar-sweetened soft drink per month. The association was slightly attenuated after adjustment for lifestyle and dietary confounders. This finding suggests that BMI accounted for about half of the excess risk. Adjustment for caloric intake in addition to BMI further attenuated the association, but sugar-sweetened soft drinks remained significantly associated with an increased risk of diabetes.

COMMENT

In this 8-year follow-up study of women, we found positive associations between sugar-sweetened beverage consumption and both greater weight gain and risk of type 2 diabetes, independent of known risk factors.

Besides their potential contribution to weight gain, sugar-sweetened soft drinks might also increase risk of type 2 diabetes because of their high amount of rapidly absorbable carbohydrates. They contain large amounts of high-fructose corn syrup, which has similar effects on blood glucose as sucrose, and consumption of sugar-sweetened soft drinks induces a fast and dramatic increase in both glucose and inulin concentrations. Sugar-sweetened soft drinks therefore contribute to a high glycemic index of the overall diet, a risk factor for diabetes in this study population and other cohort studies.

In conclusion, our findings suggest that frequent consumption of sugar-sweetened beverages may be associated with larger weight fain and increased risk of type 2 diabetes, possibly by providing excessive calories and large amounts of rapidly absorbable sugars. Public health strategies to prevent obesity and type 2 diabetes should focus on reducing sugar-sweetened beverage consumption.