Fructose-Rich Beverages and Risk of Gout in Women FREE

Gout is a common and excruciatingly painful inflammatory arthritis. Emerging evidence suggests that gout is strongly associated with metabolic syndrome and may lead to myocardial infarction,^1- 2 diabetes, and premature death.² Gout has historically been considered a male disease,^3- 4 but increasing evidence suggests a substantial disease burden of gout among elderly women (up to 5% of women >70 years old), whose representation in the general population has grown with increasing longevity.^5- 6

The increasing disease burden of gout in the United States over the last few decades (eg, an annual incidence of 16/100 000 in 1977 vs 42/100 000 in 1996⁶) coincided with a substantial increase in soft drink and fructose consumption.⁷ Although sugar-sweetened beverages contain low levels of purine (ie, the precursor of uric acid), they contain large amounts of fructose, which is the only carbohydrate known to increase uric acid levels.^8- 10 In humans, acute oral or intravenous administration of fructose results in a rapid increase in serum uric acid via accentuated degradation of purine nucleotides and increased purine synthesis.^11- 12 Furthermore, this urate-increasing effect was found to be exaggerated in individuals with hyperuricemia⁹ or a history of gout.⁸

A recent prospective study of men found that sugar-sweetened sodas, fruit juices, and fructose were associated with a substantially increased risk of gout among men.¹³ To date, no other cohort study has investigated this relationship. Furthermore, because animal experiments¹⁴ and 2 National Health and Nutrition Examination Survey (NHANES) studies have suggested that the magnitude of the urate-increasing effect of sugar-sweetened soft drinks may be weaker among women than among men,¹⁵ extrapolation of data on this potentially important risk factor for gout from men to women should be carried out with caution.

To address these issues, we prospectively evaluated the relationship between intake of fructose-rich bever-ages and fructose and incidence of gout in a cohort of 78 906 women with no history of gout.

The Nurses' Health Study was established in 1976 when 121 700 female registered nurses who were predominantly white (95%), aged 30 to 55 years, and living in 11 states completed a mailed questionnaire providing detailed information about their medical history, lifestyle, and other risk factors. The information is updated every 2 years to identify newly diagnosed diseases and the follow-up rate exceeds 90%. In 1980, a food frequency questionnaire was added and in 1984, participants were asked about intake of sodas in detail. For our analysis, we excluded women with a previous diagnosis of gout before 1984 or participants who did not complete more than 10 items on the 1984 dietary questionnaire, leaving 78 906 eligible women who were followed up from 1984 to 2006.

The Partners HealthCare System institutional review board approved this study; return of a completed questionnaire was accepted by the institutional review board as implied participant informed consent.

To assess dietary intake including soft drink intake, we used a validated food frequency questionnaire that inquired about average use of foods and beverages during the previous year.^4,16- 19 The dietary questionnaires were completed in 1980, 1984, 1986, 1990, 1994, 1998, and 2002. Starting in 1984, participants were asked how often on average during the previous year they had consumed sugar-sweetened soda (“Coke, Pepsi, or other cola with sugar,” “caffeine-free Coke, Pepsi, or other cola with sugar,” and “other carbonated beverages with sugar”) and diet sodas (“low-calorie cola with caffeine,” “low-calorie caffeine-free cola,” and “other low-calorie beverages”). Different types of fruits and fruit juices (including orange juice, apple juice, grapefruit juice, tomato juice, and other fruit juices) were also assessed.

We summed the intakes of single items to create a total of sugar-sweetened soda, diet soda, and fruit juice consumption. The participants could choose from 9 frequency responses (never, 1-3 per month, 1 per week, 2-4 per week, 5-6 per week, 1 per day, 2-3 per day, 4-5 per day, or ≥6 per day).

Nutrient intakes were computed by multiplying the frequency response by the nutrient content of the specified portion sizes.¹⁷ Values for nutrients were derived from US Department of Agriculture sources²⁰ and supplemented with information from manufacturers. Half of the disaccharide sucrose is fructose, which is split from sucrose in the small intestine.²¹ Therefore, total fructose intake is equal to the intake of free fructose plus half the intake of sucrose.²¹

Food intake assessed by this dietary questionnaire has been validated previously against two 1-week diet records in this cohort.^16,22 Specifically, 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 this cohort and were 0.84 for sugar-sweetened sweetened cola, 0.55 for other sugar-sweetened sodas, 0.73 for diet cola, 0.74 for other diet sodas, 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.^22- 23

At baseline and every 2 years thereafter, participants provided information on weight, regular use of medications (including diuretics), and medical conditions (including hypertension).¹⁹ These data have been found to be reliable in validation studies, and many studies have demonstrated the ability to predict risk of relevant future diseases. Body mass index was calculated as updated weight in kilograms divided by baseline height in meters squared.

We ascertained incident cases of gout using the American College of Rheumatology gout survey criteria, as previously described.^4,18- 19 Briefly, in 1982, 1984, 1986, 1988, 2002, and thereafter, biennial questionnaires asked whether participants had received a physician diagnosis of gout and, if so, the date of first occurrence. Starting in 2001, we mailed a supplementary questionnaire to participants with self-reported incident gout diagnosed in 1980 onward to confirm the report and to ascertain whether the cases met the American College of Rheumatology gout survey criteria.^4,18- 19,24

The primary end point in this study was incident cases of gout that met 6 or more of the 11 gout criteria (ie, >1 attack of acute arthritis, maximum inflammation developed within 1 day, oligoarthritis attack, redness observed over joints, painful or swollen first metatarsophalangeal joint, unilateral first metatarsophalangeal joint attack, unilateral tarsal joint attack, tophus, hyperuricemia, asymmetric swelling within a joint, complete termination of an attack).^4,18- 19,24

The overall response rate for the supplementary gout questionnaire was 81%, similar to that observed in the Health Professionals Follow-up Study.⁴ Two board-certified rheumatologists reviewed the medical records from a sample of 56 women from this cohort in 2001. The concordance between the diagnosis of gout using the American College of Rheumatology survey criteria²⁴ and our review of the relevant medical records was 91% (51/56), similar to that found in men in the Health Professionals Follow-up Study.⁴

We computed person-time of follow-up for each participant from the return date of the 1984 questionnaire (ie, the first questionnaire with detailed intake information on soft drinks and fruit juices) to the date of diagnosis of gout, death due to any cause, or the end of the study period (June 2006), whichever came first. Women who died or reported having gout on previous questionnaires were excluded from subsequent follow-up.

To represent long-term average intakes of fructose and fructose-rich beverages by individual participants, we used cumulative average intakes based on the dietary information from baseline to the latest point of follow-up as a time-varying variable.^{4,18- 19,25- 26} For example, the incidence of gout from 1984 through 1986 was related to the intake reported on the 1984 questionnaire, incidence from 1986 through 1990 was related to the average of intakes reported on the 1984 and 1986 questionnaires, and incidence from 1990 through 1994 was related to the average of intakes reported on the 1984, 1986, and 1990 questionnaires. Secondary analyses using only information from the baseline questionnaire (1984) yielded similar results.

We used Cox proportional hazards modeling (PROC PHREG) to estimate the relative risk (RR) of incident gout in all multivariate analyses (SAS software, version 9.1, SAS Institute Inc, Cary, North Carolina). For these analyses, soda and juice consumption were categorized into 6 groups: less than 1 serving per month, 1 per month to 1 per week, 2 to 4 per week, 5 to 6 per week, 1 per day, and 2 or more per day. Free fructose and total fructose intake were categorized into quintiles based on percentage of energy (nutrient density²⁷).

Multivariate models for soda and juice consumption were adjusted for the following variables in a time-varying manner: age (continuous), total energy intake (continuous), alcohol (none, 0.1-4.9, 5.0-9.9, 10.0-14.9, 15.0-29.9, 30.0-49.9, or ≥50.0 g/d), body mass index (<21, 21-22.9, 23-24.9, 25-29.9, 30-34.9, or ≥35), menopause status (menopausal or not), use of hormone therapy (yes or no), use of diuretics (thiazide or furosemide) (yes or no), history of hypertension (yes or no), coffee intake (0, <1, 1-3, or ≥4 cups per day), and daily mean intake of meats, seafood, dairy foods, and total vitamin C (quintiles).^4,18- 19 Similarly, we evaluated the association with fruit intake (individual fruits and total fruit) while adjusting for the same covariates and simultaneously for intake of soda and juices.

In multivariate nutrient density models for fructose intake,²⁷ we simultaneously included energy intake, percentages of energy derived from protein and carbohydrate (or nonfructose carbohydrate), intakes of vitamin C and alcohol, and other nondietary variables. The coefficients from these models can be interpreted as the estimated effect of substituting a specific percentage of energy from fructose for the same percentage of energy from nonfructose carbohydrates (or fat).^25,27 For example, to estimate the effect of substituting fructose for the equivalent energy from fat, the model included percentage of energy from nonfructose carbohydrate and total protein.

Trends in gout risk across categories of soda, juice, or fructose intake were assessed in Cox proportional hazards models by using the median values of intake for each category to minimize the influence of outliers. We conducted analyses stratified by body mass index (<30 vs ≥30), alcohol use (yes or no), and low-fat dairy intake (≤0.57 servings per day [median value] vs >0.57 servings per day) to assess possible effect modification. We tested the significance of the interaction with a likelihood ratio test by comparing a model with the main effects of each intake and the stratifying variable and the interaction terms with a reduced model with only the main effects. For all RRs, we calculated 95% confidence intervals (CIs). All P values are 2-sided, with P <.05 considered statistically significant.

During 22 years of follow-up, we documented 778 newly diagnosed cases meeting American College of Rheumatology criteria for gout (638 [82%] with podagra, 576 [74%] with hyperuricemia, 342 [44%] with tarsal joint involvement, and 109 [14%] with tophus). The characteristics of the cohort according to consumption levels of sugar-sweetened soda and free fructose at baseline are shown in Table 1. With increasing sugar-sweetened soda consumption, intake of fructose, sucrose, meat, high-fat dairy foods, and coffee tended to increase, but mean age, prevalence of menopause, and intake of low-fat dairy, fruit, and vitamin C tended to decrease (Table 1). Alcohol intake was lower in the middle categories of sugar-sweetened soda consumption. With increasing free fructose consumption, body mass index and intake of alcohol, coffee, meat, and high-fat dairy foods tended to decrease but prevalence of menopause and intake of fruit and vitamin C tended to increase (Table 1).

Increasing intake of sugar-sweetened soda was associated with increasing risk of gout (P<.001 for trend) (Table 2). Compared with consumption of less than 1 serving per month, the multivariate RR of gout was 1.74 (95% CI, 1.19-2.55) for 1 serving per day and 2.39 (95% CI, 1.34-4.26) for 2 or more servings per day (P<.001 for trend). The corresponding absolute risk differences were 36 and 68 cases per 100 000 person-years. In contrast, diet soda intake was not associated with risk of gout (P = .27 for trend).

Orange juice intake was associated with risk of gout (Table 3). Of note, orange juice was by far the highest contributor of free fructose intake (17%) among juices in this cohort, followed by apple juice at 2.9% and other juices at 2.6% at the midpoint of follow-up. Compared with women who consumed less than a glass (6 oz) of orange juice per month, the multivariate RR for gout was 1.41 (95% CI, 1.03-1.93) for 1 serving per day and 2.42 (95% CI, 1.27-4.63) for 2 or more servings per day (P = .02 for trend) (Table 3). The corresponding absolute risk differences were 14 and 47 cases per 100 000 person-years, respectively. There was no significant trend between intake of other juices and risk of gout (multivariate P = .11). No other individual fructose-rich food item (eg, apples or oranges) was significantly associated with risk of gout. Similarly, total fruit intake was not associated with risk of gout (P = .80 for trend).

Increasing fructose intake was associated with increasing risk of gout (Table 4). Compared with women in the lowest quintile of free fructose intake, the multivariate RR of gout in the highest quintile was 1.43 (95% CI, 1.09-1.88) (P = .02 for trend) when substituting fructose for the equivalent energy from fat. The corresponding RR increased after we adjusted for total carbohydrate intake to reflect the substitution effect of fructose for other types of carbohydrates (multivariate RR, 1.62; 95% CI, 1.20-2.19) (P = .004 for trend). The corresponding absolute risk difference was 28 cases per 100 000 person-years. Similar trends were observed with intake of total fructose (ie, free fructose plus half the intake of sucrose), although the magnitudes of associations tended to be smaller (Table 4). When we examined fructose intake as a continuous variable, the multivariate RR for a 5% increment in energy from free fructose, compared with equivalent energy intake from other types of carbohydrates, was 1.86 (95% CI, 1.44-2.40) and the corresponding RR for total fructose was 1.47 (95% CI, 1.20-1.80).

We also conducted stratified analyses to evaluate whether the association between sweetened soda and fructose consumption and risk of gout varied according to body mass index, alcohol use, and dairy intake. Relative risks from these stratified analyses consistently suggested associations similar to those from main analyses, and there was no significant interaction with these variables (all P ≥.14 for interaction) (Table 5 and Table 6).

In this large prospective study of women, we found that risk of incident gout increased with increasing intake of sugar-sweetened soda. In contrast, diet soda intake was not associated with risk of incident gout. Women who consumed 1 serving per day of sugar-sweetened soda had a 74% higher risk of incident gout and women who consumed 2 servings or more per day had a 2.4-fold increased risk. Similarly, women who consumed 2 servings or more of orange juice showed a 2.4-fold increased risk of incident gout. Furthermore, risk of gout was significantly increased with increasing intake of fructose, the main ingredient thought to cause the increased risk. These associations were independent of risk factors for gout such as body mass index, age, hypertension, menopause, diuretic use, alcohol, and intake of dairy, meat, seafood, coffee, and vitamin C. These findings confirm the associations observed in the recent prospective study of men¹³ and provide the first prospective evidence among women that fructose and fructose-rich beverages are important risk factors to be considered in the primary prevention of gout.

Although the RRs of gout associated with fructose-rich beverages among women were substantial, the corresponding absolute risk differences were modest given the low incidence rate of gout among women. For example, the magnitudes of RRs associated with sugar-sweetened sodas or orange juice were comparable with those associated with alcoholic beverages (RR for ≥2 servings per day, 1.60 for liquor vs 2.51 for beer) among men.¹⁸ However, the corresponding absolute risk differences were less than 1 case per 1000 person-years. Although the RR data suggest a substantial biologic link, the risk difference data suggest that their contribution to the risk of gout in the population is likely modest given the low incidence rate among women. Because the urate-increasing effect of fructose is greatest in patients with gout and hyperuricemia,^8- 10,28 our findings may be even more relevant in those patients.

Previous animal experiments^14,29- 30 and NHANES studies^15,31 have suggested that the magnitude of the urate-increasing effect of fructose or sugar-sweetened sodas may be weaker among females than among males. For example, an analysis based on NHANES III found that the increase in serum uric acid level associated with sugar-sweetened soda intake was significantly larger among men than women, although the association among women was still statistically significant.¹⁵ This potential sex difference has been thought to be due to sex hormones because studies in rats have shown that female sex hormones protect against the development of hyperinsulinemia associated with high fructose intake.^14,29- 30 Because hyperinsulinemia decreases renal excretion of urate and correlates with higher serum uric acid levels,³² the protective effect of estrogen may lead to an attenuated effect of fructose on serum uric acid levels. Nevertheless, as gout among women occurs predominantly after menopause, when the female hormonal influence substantially declines, the sex difference of the fructose effect on the risk of gout may be less apparent than that on serum uric acid levels observed in the general population that included premenopausal women.

Fructose induces uric acid production by increasing adenosine triphosphate (ATP) degradation to adenosine monophosphate, a uric acid precursor (Figure).^12,28,33 Fructose phosphorylation in the liver uses ATP, and the accompanying phosphate depletion limits regeneration of ATP from adenosine diphosphate, which in turn serves as substrate for the catabolic pathway to uric acid formation.³⁴ Thus, within minutes after fructose infusion, plasma (and later urinary) uric acid concentrations are increased.²⁸ In conjunction with purine nucleotide depletion, rates of purine synthesis de novo are accelerated, thus potentiating uric acid production.¹¹ In contrast, glucose and other simple sugars do not have the same effect.³⁵

Furthermore, fructose could indirectly increase serum uric acid level and risk of gout by increasing insulin resistance and circulating insulin levels.³⁶ Experimental studies in animal models and from short-term feeding trials among humans suggest that higher fructose intake contributes to insulin resistance, impaired glucose tolerance, and hyperinsulinemia.^23,37- 38 In contrast, glucose intake had no similar adverse effects.³⁸

Our findings have practical implications for the prevention of gout in women. As conventional dietary recommendations for gout have focused on restriction of purine intake, low-purine diets are often high in carbohydrates, including fructose-rich foods.³⁹ Our data provide prospective evidence that fructose poses an increased risk of gout among women, thus supporting the importance of reducing fructose intake. Interestingly, this recommendation is consistent with Osler's diet prescription as a means to prevent gout more than 100 years ago: “The sugar should be reduced to a minimum.”^35,40 Furthermore, because fructose intake is associated with increased serum insulin levels, insulin resistance, and increased adiposity,^23,37- 38 the overall negative health effect of fructose is expected to be larger in women with a history of gout, 70% of whom have metabolic syndrome.³²

Several strengths and potential limitations of our study deserve comment. Our study had a large number of cases of confirmed incident gout among women, and dietary data including beverage and fructose intake information were prospectively collected and validated. Although there was a relatively large number of cases in the highest fructose quintile groups, the numbers in the top intake categories of fructose-rich beverage items were small. Nevertheless, it was reassuring that the next highest categories also showed significant positive associations with a dose-response relationship. Potential biased recall of diet was avoided in this study because intake data were collected before the diagnosis of gout. Because dietary consumption was self-reported by questionnaire, some misclassification of exposure is inevitable. However, self-reported dietary consumption has been extensively validated in subsamples of this cohort,^16,22 and any remaining misclassification would have likely biased the results toward the null. The use of repeated dietary assessments in the analyses not only accounts for changes in dietary consumption over time but also decreases measurement error. The validity of gout ascertainment in this cohort and our companion male cohort^4,18- 19 has been documented by the high degree of concordance with medical record review.

The restriction to registered nurses in our cohort is both a strength and a limitation. The cohort of well-educated women minimizes potential for confounding associated with socioeconomic status, and we were able to obtain high-quality data with minimal loss to follow-up. Although the absolute rates of gout and related measures, as well as distribution of fructose intake, may not be representative of a random sample of US women, the biological effects of fructose intake on gout (as reflected in RRs) should be similar. Our findings are most directly generalizable to middle-aged and elderly white women with no history of gout. Since the prevalence of risk factors for gout and its incidence tend to be higher in the general population and among African Americans, the magnitude of the absolute risk increase associated with these beverages might be greater than the increase we observed.

In conclusion, our findings provide prospective evidence that consumption of sugar-sweetened sodas, orange juice, and fructose is associated with an increased risk of incident gout among women, although their contribution to the risk of gout in the population is likely modest given the low incidence rate among women. In contrast, diet soda intake is not associated with the risk of gout. Physicians should be aware of the potential effect of these beverages on the risk of gout, a common and excruciatingly painful arthritis.