Vernarelli JA, Lambert JD. Tea consumption is inversely associated with weight status and other markers for metabolic syndrome in US adults. Eur J Nutr. July 10, 2012; [epub ahead of print]. doi: 10.1007/s00394-012-0410-9.
After water, tea (Camellia sinensis) is the most commonly consumed beverage worldwide. The three major types of tea—black, oolong, and green—differ in the ways they are processed, their chemical composition, and their consumption patterns. Tea and tea polyphenols have been studied for their potential role in the prevention of cancer, heart disease, neurodegenerative disease, and other chronic conditions.
Laboratory and human intervention studies suggest that tea and tea polyphenols may help prevent obesity and metabolic syndrome (MetS). "To our knowledge," say the authors, "no studies have been conducted to determine the association between tea consumption and multiple markers for MetS in U.S. adults."
They conducted a study to determine the relationship between tea consumption (including black, green, and oolong; both hot and cold) and markers for MetS in a representative sample of adults from the 2003-2006 National Health and Nutrition Examination Survey (NHANES) data. Using the data, they examined the association of tea consumption with multiple markers for MetS: body mass index (BMI), waist circumference (WC), fasting glucose, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), serum triglycerides (TGs), and C-reactive protein (CRP), a marker of systemic inflammation.
For this analysis, all adults who were aged ≥18 years were initially included (n=11,183). After excluding persons for various reasons, a final sample of 6,472 adults (53% female) was used to analyze tea consumption and anthropometric measures. In a small subset of those, 3,118 fasting blood samples were collected to measure serum insulin, serum glucose, TGs, LDL-C, HDL-C, and TC.
Participants were categorized by their consumption for both hot and iced tea: nonconsumers, infrequent consumers (≤1 cups weekly), weekly consumers (2-6 cups weekly), consumers of 1 cup daily, or consumers of multiple cups daily.
The participants were classified as lean (BMI≤24.9 kg/m2), overweight (BMI=25.0-29.9 kg/m2), or obese (BMI≥30 kg/m2). Body fatness was evaluated by using WC and skinfold thickness.
The authors used multivariate regression to evaluate the association of tea consumption with health outcomes related to obesity. Sex-specific analysis accounted for the natural differences in body composition and caloric needs between men and women.
The racial breakdown of the participants was similar to the U.S. population; 76% were white. About two-thirds were overweight or obese. Of the total number of participants, 57% reported some sort of hot tea consumption, 9% consumed hot tea daily, and 70% drank iced tea.
To evaluate the relationship between tea and body weight independently of other dietary factors, the authors examined the macronutrient intake, energy intake, caffeine intake, and percentage of dietary fat. They reported no significant differences in caffeine intake or macronutrient intake among any of the categories of hot tea or iced tea consumption. Because women who drank multiple cups of hot tea daily had significantly higher total energy intake than nonconsumers, and men who drank hot tea daily had significantly lower total energy intake and lower sugar intake than nonconsumers, the total energy and total sugar intakes were included as covariates in all regression models. Alcohol intake was also included in all regression models for the same reason.
The authors report that tea consumption was inversely associated with BMI in both men and women after controlling for age, race, income, education, smoking status, total energy intake, sugar intake, alcohol intake, herbal tea consumption, and physical activity. Women in the highest category of tea consumption had the lowest BMI (26.2 kg/m2 vs. 28.5 kg/m2 for nonconsumers); the same relationship was observed in men (25.4 kg/m2 vs. 27.9 kg/m2). A decrease in WC was observed in both men and women, with a stronger association found among men.
Iced tea consumption was associated with a significant increase in WC (P=0.0002) and BMI (P=0.004) in women who were multiple-cup drinkers, even after controlling for the covariates. In men, nonconsumers had a lower BMI (P=0.08) and a lower WC (P=0.03) than men who consumed multiple cups of iced tea daily, but no other relationships existed.
In both men and women, skinfold thickness increased with increased iced tea consumption. Hot tea consumption was inversely associated with fasting glucose in women, but not in men; no association was observed with iced tea consumption in either sex. Different associations were observed in men and women regarding lipid profiles. In women, no association was reported between markers of dyslipidemia and hot tea consumption; however, HDL-C and TG levels decreased as iced tea consumption increased.
Men who drank multiple cups of hot tea daily had higher HDL-C levels and significantly lower TG levels than nonconsumers. Iced tea consumption in men was not associated with changes in any of the lipid markers.
A significant negative association between hot tea consumption and CRP was seen in both men and women (P for trend<0.001 for men and P for trend<0.01 for women). No association between iced tea consumption and CRP was reported. The results suggest that hot tea consumption may reduce the risk for cardiovascular events, although the body of epidemiological data on the cardioprotective benefits of tea consumption remains mixed.1
After examining the relationship between hot and iced tea consumption and markers for MetS, the authors report a significant inverse association between hot tea consumption and obesity and inflammation in both men and women. They also report that among iced tea consumers, an increase in BMI, WC, and inflammatory markers was observed. "These findings demonstrate that the health benefits of tea consumption may occur only when tea is consumed in a traditional manner, and that iced tea may provide no health benefit to consumers. These results support the potential of tea as a modulator of body weight and indicate the need for further controlled, intervention studies to compare the effects of black, oolong, and green tea on body weight and body fat," they conclude. It should be noted that many of the cold tea products available on the market contain sugar. Also, several cups of tea (without sweetener) per day over an extended period of time may be the most beneficial for maintaining a healthy body.