Association of Hot Tea Consumption with Regional Adiposity Measured by Dual-Energy X-Ray Absorptiometry in NHANES 2003-2006
Abstract
Objective
This study aimed to investigate the potential antiobesity benefits of hot tea consumption at the population level.
Methods
Using data from the National Health and Nutrition Examination Survey (NHANES) 2003-2006, the association between hot tea consumption and dual-energy x-ray–measured body fat was examined in a large representative sample of US adults (n = 5,681, 51.9% women).
Results
Compared with non–tea drinkers, men who consumed 0.25 to 1 cup per day of hot tea had 1.5% (95% CI: 0.4% to 2.6%) and 1.7% (95% CI: 0.4% to 3.0%) less total and trunk body fat, respectively. The associations were stronger among men 45 to 69 years old compared with younger men (20-44 years). For men who consumed 1 or more cups per day of hot tea, lower total (−1.2%, 95% CI: −2.3% to −0.2%) and trunk body fat (−1.3%, 95% CI: −2.6 to −0.1%) was observed among men 45 to 69 years old only. In women, those who drank 1 or more cups per day had 1.5% lower (95% CI: −2.7% to −0.3%) trunk body fat compared with non–tea drinkers.
Conclusions
Consumption of hot tea might be considered as part of a healthy diet in order to support parameters associated with metabolic health and may be particularly important in older male age groups in supporting reduced central adiposity.
Study Importance
What is already known?
- Regular consumption of tea has been associated with reduced incidence of various cancers and cardiometabolic risk factors.
- Tea catechins have been proposed to have antiobesity properties, with a meta-analysis highlighting a small yet positive effect on weight loss and weight maintenance.
- There has been minimal research investigating whether total and central body fat levels are typically lower based on regular consumption of tea in large-scale population studies.
What does this study add?
- This study provides evidence suggesting that consumption of hot tea is associated with reduced trunk body fat in both men and women.
- Consumption of hot tea might be considered as part of a healthy diet in order to support parameters associated with metabolic health and may be particularly important in older male age groups in supporting reduced central adiposity.
Introduction
Tea beverages are among the most popular daily drinks consumed globally, second only to water. Global tea consumption in 2018 was estimated at 273 billion liters per annum and projected to increase to 297 billion liters by 2021 (three times as much as coffee consumption rates) (1). The Tea Association of the USA estimates that some 159 million Americans consume tea on a daily basis (2), partly because of the beverage satisfaction as well as perceived health benefits (3-5). All tea comes from the leaves or buds of the Camellia sinensis plant and, based on fermentation processing, results in the main black, white, oolong, green, yellow, and pu-erh tea classifications.
Tea, particularly green tea, contains phytonutrient phenolic compounds, or flavonoids (namely the flavan-3-ols and flavonols) (6), which are well known for their antioxidative, anti-inflammatory, and anticarcinogenic health benefits (7). The antioxidant properties of tea were shown to be affected by both temperature (infusion with hot water) and time of steeping (e.g., steeped ice tea) (8). As such, regular consumption of tea has been associated with reduced incidence of various cancers and cardiometabolic risk factors (9-12). The increase in plasma antioxidant capacity associated with tea consumption typically occurs within 60 minutes of consumption and rapidly reduces within 90 minutes (13), hence supporting the potential benefits of regular daily consumption. Of note, the addition of milk to tea appears to limit or minimize its antioxidant potential (13).
With increasing rates of overweight and obesity in the United States, there is current interest in strategic practices to support weight management in conjunction with both caloric restriction and exercise regimens. Tea catechins have been proposed to have antiobesity properties, with a 2009 meta-analysis highlighting a small yet positive effect on weight loss and weight maintenance (14). However, the authors also indicated that prior habitual caffeine intake and/or ethnicity may be potential moderators of catechin effectiveness. The majority of research investigating antiobesity properties of tea consumption have largely focused on green tea. Mechanistically, tea catechins (including caffeine) were shown to enhance 24-hour energy expenditure, indicating a thermogenic effect favoring fat oxidation over carbohydrate oxidation (15). Regular consumption of a green tea catechin beverage (containing 625 mg of catechins and 39 mg of caffeine) has been shown to favorably improve body composition, assessed via dual x-ray absorptiometry (DXA) and computed tomography, through reductions in both total and subcutaneous abdomen fat area as well as reduce fasting serum triglycerides (16, 17). While it is possible that an increased hepatic fat oxidation rate may contribute to the reduction in central fat storage observed in these studies, there has been minimal research investigating whether total and central body fat levels are typically lower based on regular consumption of tea in large-scale population studies. This has potential implications considering the cardiometabolic risks associated with increased visceral adiposity. Therefore, the focus of this study was to assess the associations of regular hot tea consumption with total and central (trunk) body fat levels in US adults.
Methods
Study population
The National Health and Nutrition Examination Survey (NHANES) is a major study conducted by the National Center for Health Statistics, collecting nationally representative samples to monitor the health, nutritional status, and potential risk factors for diseases among noninstitutionalized civilians in the United States (18). The data are collected on a continual basis and released in 2-year increments. Survey participants complete a written informed consent form as well as a household interview and undergo a physical examination at the mobile examination center. We extracted and aggregated data on sociodemographic characteristics, DXA, dietary patterns, medical conditions, and lifestyle behaviors in the two waves of 2003-2004 and 2005-2006 among those aged 20 to 69 years because the DXA examination was carried out only on this age group and both hot tea consumption and DXA data were measured at the same time in these waves only (19).
Assessment of exposure
The NHANES food frequency questionnaire (FFQ) was developed by the National Cancer Institute and revised from the widely used National Cancer Institute Diet History Questionnaire, measuring 124-item food frequency in nutritional epidemiology research (20). Daily hot tea consumption frequency over the past 12 months was assessed in 10 categories, ranging from 0 to 6 or more cups per day, and collapsed into four groups (no hot tea, 0-0.25, 0.25-1, 1 or more cups/day) (21). These categories have been previously used in one other study (12). Additional questions on decaffeinated hot tea (“How often was the hot tea you drank decaffeinated or herbal tea?”) and frequency of adding sugar or honey, artificial sweeteners, and nondairy creamer were used to control potential confounding components.
DXA scan
The whole-body DXA scans were obtained using a Hologic QDR 4500A fan-beam densitometer (Hologic, Inc., Bedford, Massachusetts) in accordance with the manufacturer's manual (19). Pregnant or menstruating women, those who self-reported body mass greater than 300 lb or height greater than 6′5″, and those who had a self-reported history of radiographic contrast material (barium) use in the past 7 days were excluded because of their ineligibility for the DXA examination (22). The DXA scan results were reviewed and analyzed using standard radiologic techniques and study-specific protocols developed for NHANES at the University of California, San Francisco, Department of Radiology (Hologic Discovery software version 12.1 was used to analyze DXA exams and provided body composition data). The magnitudes and distributions of body fat were represented using fat percentage of the trunk (only the trunk area of the human body) and fat percentage of the total body (including head, limbs, and trunk area of the body).
Covariates
Self-reported sociodemographic characteristics included age, gender, race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and others), annual household income ($25,000 or less, $25,000 to $74,999, and $75,000 or above), and education (less than high school, high school, and above high school). Lifestyle behaviors included physical activity, smoking status, TV watching (hours/day), computer use (hours/day), and intention to lose or control weight. Physical activity level was defined by whether one participated in moderate-to-vigorous physical activity in the past 30 days or not. We used TV watching time and computer use time to reflect the sedentary behaviors (23). Comorbidity was identified by self-reports of the following six highly prevalent excess adiposity–associated chronic conditions: hypertension, high blood cholesterol, coronary heart diseases, osteoarthritis, stroke, and diabetes (24). Participants’ weight and height were measured according to standard procedures during the physical examination. BMI was calculated as weight in kilograms divided by height in meters squared and categorized into underweight (< 18.5), normal weight (18.5-24.9), overweight (25.0-29.9), and obesity (≥ 30) based on the standard classification. Last, we derived data on dietary covariates from both the FFQ (including alcoholic beverages [beer, liquor, wine, and coffee consumption]), dietary supplement use (epigallocatechin gallate and green tea extracts), and 24-hour recall data (including total calorie intake and the Healthy Eating Index 2010) (20).
Statistical analysis
We used the NHANES DXA examination data set as released by the National Center for Health Statistics (https://wwwn.cdc.gov/nchs/nhanes/dxa/dxa.aspx). Because missing DXA data were related to age, BMI, weight, and height, and possibly to other characteristics, participants with missing data could not be considered as a random subset of the original sample. As such, analytic results could be biased toward participants with the least amount of missing data (19, 20). To reduce potential bias, multiple imputation was applied at the National Center for Health Statistics to reflect the additional variability caused by the use of imputed values for the missing data (19). In brief, each participant underwent five DXA scans. The NHANES program imputed any missing scan for individuals based on a complex list of variables, including sociodemographic characteristics, geographic variables, body measurements, health status, dietary pattern, medication use, and laboratory test results. The five completed DXA data sets were collapsed into a single file for each cycle and released to the public (25). We followed NHANES technical guideline to conduct the present analyses. Because of established biological gender differences in metabolism (26, 27), we conducted all analyses separately by gender. We further conducted all the analyses among each age group because age is an important factor of changes in energy metabolism and lifestyle behaviors (26). We used 45 years old as the cutoff for the age group because it is a cutoff for middle adulthood (28). It is also the approximated mean age of our sample population. First, we calculated the descriptive characteristics of study population according to frequency of daily hot tea consumption among men and women. Second, we examined the association of frequency of daily hot tea consumption with body fat percentage using age-adjusted and multivariable-adjusted linear regression models. SAS-callable SUDAAN version 11.0 (RTI International, Research Triangle Park, North Carolina) was adapted for the complex survey design and it analyzed a multiply imputed data set to reduce bias. Sample weights adhered to the National Center for Health Statistics recommendations (29). Our estimation procedure was carried out five times, once for each version of the completed data. We conducted sensitivity analyses by restricting the study sample to those who self-reported drinking caffeinated tea more than half of the time. All statistical tests were two-sided, and statistical significance was set at P < 0.05.
Results
In NHANES 2003-2006, 13,760 eligible participants had reliable data on DXA. After excluding 5,726 individuals under 20 years old and 2,353 participants without information on hot tea consumption, 5,681 adults aged ≥ 20 years (51.9% women) were included in the final analysis. Characteristics of the participants are presented according to frequency of daily tea consumption and gender (Table 1). In both men and women, frequent hot tea drinkers (1 or more cups/day) were older than those who were less frequent (0-0.25 cup, 0.25-1 cup/day) consumers and those who reported no hot tea consumption. In addition, “other” racial/ethnic groups were more likely to report consuming one or more cups of tea (men: 14.8%; women: 20.0%) compared with non-Hispanic white, non-Hispanic black, and Hispanic groups (men: all groups ≤ 7.7%; women: all groups ≤ 8.9%). Overall, frequent hot tea drinkers were more likely to have a healthy diet compared with nondrinkers (Healthy Eating Index 2010 score, men: 56.6 vs. 46.6; women: 57.1 vs. 47.9). The weighted means of body fat percentage (total and trunk) by weight status are shown in Supporting Information Table S1.
| Men (n = 2,734) | Women (n = 2,947) | |||||||
|---|---|---|---|---|---|---|---|---|
| No hot tea (n = 1,412) | 0-0.25 cup (n = 910) | 0.25-1 cup (n = 206) | 1+ cup (n = 206) | No hot tea (n = 1,073) | 0-0.25 cup (n = 1,116) | 0.25-1 cup (n = 396) | 1+ cup (n = 352) | |
| Age (y) | ||||||||
| Mean (SE) | 44.8 (0.4) | 46.0 (0.7) | 48.1 (1.1) | 50.9 (1.5) | 44.4 (0.7) | 46.2 (0.6) | 49.6 (1.2) | 51.7 (0.9) |
| Race/ethnicity (%) | ||||||||
| Non-Hispanic white | 53.3 | 34.4 | 6.2 | 6.1 | 35.4 | 39.9 | 13.3 | 11.4 |
| Non-Hispanic black | 48.8 | 35.5 | 8.0 | 7.7 | 34.8 | 41.6 | 14.8 | 8.9 |
| Hispanic | 59.8 | 26.7 | 7.5 | 6.0 | 41.7 | 36.2 | 11.2 | 10.9 |
| Other | 38.1 | 39.2 | 8.0 | 14.8 | 37.0 | 31.6 | 11.4 | 20.0 |
| Annual household income (%) | ||||||||
| <$25,000 | 54.6 | 30.0 | 8.8 | 7.1 | 42.3 | 32.0 | 11.7 | 14.1 |
| $25,000-74,999 | 57.0 | 32.7 | 5.3 | 5.1 | 36.8 | 40.0 | 13.6 | 9.0 |
| ≥$75,000 | 54.8 | 38.2 | 7.2 | 8.8 | 29.2 | 44.5 | 14.2 | 12.2 |
| Education (%) | ||||||||
| <High school | 64.8 | 22.3 | 6.7 | 6.2 | 48.2 | 28.0 | 11.4 | 12.5 |
| High school | 65.1 | 26.6 | 3.8 | 4.5 | 42.6 | 37.3 | 10.4 | 9.7 |
| >High school | 43.6 | 40.7 | 7.9 | 7.9 | 30.3 | 42.9 | 14.8 | 12.0 |
| MVPA (%) | ||||||||
| No | 61.1 | 27.6 | 6.0 | 5.3 | 44.6 | 33.7 | 11.3 | 10.4 |
| Yes | 49.2 | 36.7 | 6.8 | 7.3 | 32.1 | 41.8 | 14.0 | 12.1 |
| Smoking status (%) | ||||||||
| Never | 49.4 | 35.5 | 8.2 | 6.9 | 34.2 | 39.7 | 15.2 | 11.0 |
| Former | 47.8 | 38.4 | 5.1 | 8.7 | 30.0 | 41.6 | 13.0 | 15.3 |
| Current | 62.9 | 27.1 | 5.6 | 4.4 | 47.1 | 35.5 | 8.0 | 9.7 |
| Diabetes (%) | ||||||||
| No | 52.8 | 33.9 | 6.6 | 6.7 | 35.8 | 39.5 | 13.1 | 11.5 |
| Yes | 51.9 | 34.8 | 6.7 | 6.7 | 39.0 | 35.6 | 14.0 | 11.5 |
| TV watching (h/day) | ||||||||
| Mean (SE) | 2.5 (0.05) | 2.3 (0.06) | 2.2 (0.11) | 2.1 (0.12) | 2.4 (0.07) | 2.2 (0.06) | 2.2 (0.08) | 2.3 (0.09) |
| Computer use (h/day) | ||||||||
| Mean (SE) | 0.8 (0.04) | 0.9 (0.06) | 0.9 (0.07) | 0.8 (0.07) | 0.7 (0.04) | 0.8 (0.03) | 0.8 (0.07) | 0.7 (0.06) |
| HEI-2010 | ||||||||
| Mean (SE) | 46.6 (0.4) | 51 (0.8) | 53.2 (1.4) | 56.6 (1.2) | 47.9 (0.7) | 52.6 (0.5) | 56.7 (1.0) | 57.1 (0.9) |
- All estimates weighted to be nationally representative.
- MVPA, moderate-to-vigorous physical activity; HEI-2010, Healthy Eating Index 2010.
The associations of hot tea consumption with body fat percentage are presented in Table 2 and Supporting Information Table S2 for men and Table 3 and Supporting Information Table S3 for women. Among men, those who drank 0.25 to 1 cup per day had the lowest body fat percentage after adjusting for multiple covariates across all age groups. For example, compared with non–tea drinkers, men who consumed 0.25 to 1 cup per day of hot tea had 1.5% (95% CI: 0.4% to 2.6%) and 1.7% (95% CI: 0.4% to 3.0%) less total body fat percentage and trunk body fat percentage, respectively. However, there was no significant difference in body fat between nondrinkers and those drinking 1 or more cups per day. With respect to women, those drinking 1 or more cups per day of hot tea had the lowest body fat percentage (age-adjusted β-coefficient, total fat percentage: −2.3% [95% CI: −3.2% to −1.4%]; trunk fat percentage: −3.3% [95% CI: −4.5% to −2.1%]). With the further adjustment, women participants who drank 1 or more cups per day had −1.5% lower (95% CI: 0.3% to 2.7%) trunk body fat percentage.
| β-coefficient (95% CI) | ||||||
|---|---|---|---|---|---|---|
| All ages | 20-44 years | 45-69 years | ||||
| Age adjusted | MV adjusteda | Age adjusted | MV adjusteda | Age adjusted | MV adjusteda | |
| Total body fat, % | ||||||
| None | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] |
| 0-0.25 cup/day | −0.8 (−1.4 to −0.2) | −0.7 (−1.3 to −0.1) | −1.4 (−2.3 to −0.5) | −1.4 (−2.2 to −0.5) | −0.3 (−1.0 to 0.5) | −0.1 (−0.9 to 0.6) |
| 0.25-1 cup/day | −2.3 (−3.4 to −1.3) | −1.5 (−2.6 to −0.4) | −2.4 (−4.1 to −0.8) | −1.2 (−2.9 to 0.5) | −2.2 (−3.5 to −0.9) | −1.6 (−3.0 to −0.3) |
| 1+ cup/day | −1.5 (−2.5 to −0.5) | −0.7 (−1.6 to 0.3) | −1.5 (−3.3 to 0.3) | −0.3 (−2.3 to 1.8) | −1.3 (−2.5 to −0.1) | −1.2 (−2.3 to −0.2) |
| Trunk body fat, % | ||||||
| None | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] |
| 0-0.25 cup/day | −1.0 (−1.7 to −0.3) | −0.8 (−1.5 to −0.1) | −2.0 (−3.0 to −0.9) | −1.8 (−2.8 to −0.8) | −0.2 (−1.1 to 0.7) | 0.01 (−0.8 to 0.8) |
| 0.25-1 cup/day | −2.7 (−4.0 to −1.5) | −1.7 (−3.0 to −0.4) | −3.2 (−5.2 to −1.3) | −1.7 (−3.6 to 0.2) | −2.3 (−3.8 to −0.8) | −1.5 (−3.0 to 0) |
| 1+ cup/day | −1.7 (−2.9 to −0.5) | −0.7 (−1.9 to 0.4) | −1.6 (−4.0 to 0.7) | −0.1 (−2.6 to 2.3) | −1.5 (−2.9 to −0.1) | −1.3 (−2.6 to −0.1) |
- a All MV-adjusted models adjusted for age (continuous), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, Asian, others), household income, leisure time physical activity, education level, smoking status, comorbidity (hypertension, high blood cholesterol, coronary heart diseases, osteoarthritis, stroke, diabetes), added sugar/creamer/milk use, sugar-added beverages, alcohol (wine, beer, liquor), coffee, iced tea, dietary supplement use (epigallocatechin gallate, green tea extracts), Healthy Eating Index 2010 (continuous), and intention to lose/control weight.
- MV, multivariable.
| β-coefficient (95% CI) | ||||||
|---|---|---|---|---|---|---|
| All ages | 20-44 years | 45-69 years | ||||
| Age adjusted | MV adjusteda | Age adjusted | MV adjusteda | Age adjusted | MV adjusteda | |
| Total body fat, % | ||||||
| None | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] |
| 0-0.25 cup/day | −0.9 (−1.6 to −0.3) | −0.1 (−0.7 to 0.6) | −1.3 (−2.2 to −0.3) | 0.1 (−1.0 to 1.1) | −0.6 (−1.6 to 0.4) | −0.3 (−1.2 to 0.7) |
| 0.25-1 cup/day | −1.3 (−2.2 to −0.4) | −0.1 (−1.1 to 1.0) | −1.7 (−3.5 to 0.1) | 0.2 (−1.4 to 1.8) | −1.0 (−2.0 to −0.1) | −0.3 (−1.4 to 0.8) |
| 1+ cup/day | −2.3 (−3.2 to −1.4) | −0.8 (−1.7 to 0.1) | −3.3 (−4.8 to −1.8) | −1.0 (−2.6 to 0.5) | −1.7 (−2.8 to −0.5) | −0.7 (−1.8 to 0.4) |
| Trunk body fat % | ||||||
| None | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] | 0 [Reference] |
| 0-0.25 cup/day | −1.1 (−2.0 to −0.2) | −0.01 (−0.7 to 0.7) | −1.7 (−2.9 to −0.4) | −0.02 (−1.3 to 1.3) | −0.7 (−1.9 to 0.6) | −0.02 (−1.0 to 0.9) |
| 0.25-1 cup/day | −1.6 (−2.8 to −0.3) | −0.01 (−1.4 to 1.3) | −2.2 (−4.5 to 0.1) | 0.4 (−1.7 to 2.4) | −1.2 (−2.5 to 0.1) | −0.3 (−1.7 to 1.1) |
| 1+ cup/day | −3.3 (−4.5 to −2.1) | −1.5 (−2.7 to −0.3) | −4.7 (−6.8 to −2.6) | −1.9 (−4.0 to 0.1) | −2.4 (−3.6 to −1.1) | −1.3 (−2.7 to 0.1) |
- a All MV-adjusted models adjusted for age (continuous), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, Asian, others), household income, leisure time physical activity, education level, smoking status, menopause status, comorbidity (hypertension, high blood cholesterol, coronary heart diseases, osteoarthritis, stroke, diabetes), added sugar/creamer/milk use, sugar-added beverages, alcohol (wine, beer, liquor), coffee, iced tea, dietary supplement use (epigallocatechin gallate, green tea extracts), Healthy Eating Index 2010 (continuous), and intention to lose/control weight.
- MV, multivariable.
Our findings were similar when restricting the study sample to those who self-reported drinking caffeinated tea more than half of the time in sensitivity analyses (data not reported).
Discussion
This study provides epidemiological evidence that regular hot tea consumption may be associated with reduced body fat levels. After adjustment for a range of sociographic characteristics, health behaviors, comorbidity status, and other dietary covariates, men who reported consuming 0.25 to 1 cup of hot tea per day and women who consumed 1 or more cups of hot tea per day had a significantly lower total body fat percentage than those who reported no hot tea consumption (1.5% and 0.8% lower, respectively). Age-stratified analyses indicated a stronger association between hot tea consumption and body fat in older (45-69 years old) than younger (20-44 years old) men, but no notable differences were noted by age in women. The findings therefore suggest a potential benefit of regular tea consumption, particularly in men 45 to 69 years old.
A similar pattern was also established between hot tea consumption and trunk body fat reduction. In the multivariable-adjusted model, men who reported consuming up to 1 cup of hot tea per day had a significantly lower trunk body fat percentage compared with those who reported no hot tea consumption (1.7% and 1.5% lower, respectively). These associations attenuated to null among younger (20-44 years old) men yet remained significant among older (45-69 years old) men. These differences between age groups suggest that the effect of tea in body fat reduction may be a long-term process (12). Overall, the findings suggest an association of regular hot tea consumption with adiposity, particularly for men, and that volumes consumed in excess of 1 cup a day are more likely associated with lower trunk body fat, with the exception of younger males (20-44 years old), in which lower volumes may suffice.
These findings support the contention that regular hot tea consumption, even in relatively small volumes, may provide pertinent cardiometabolic health benefits through a modulation in body fat storage (12). This supports a meta-analysis indicating that catechins found in tea, particularly green tea, have a small positive effect on both weight loss and weight maintenance (14). However, in the current study, factors such as ethnicity and habitual caffeine intake, which were proposed to be moderators of catechin availability (14), were taken into consideration using multivariable-adjusted models. Despite potential moderators, regular hot tea consumption was associated with both lower total body fat and trunk fat in men and women. This supports previous findings highlighting that regular hot tea consumption was associated with lower body weight, subcutaneous skinfold measures, and BMI in a US population cohort (12). In contrast, iced tea consumption was associated with negative modulation of inflammatory and cardiovascular disease risk biomarkers aligned with development of metabolic syndrome (12). In the current study, consumption of > 1 cup of hot tea per day was also associated with lower prevalence of diabetes in both men and women as well as higher dietary quality (based on the Healthy Eating Index 2010). This suggests that regular tea consumption may be associated with other lifestyle or dietary choices in line with improved health status and may be an important constituent of a healthy diet.
In terms of the potential antiobesity effects of tea, the majority of research has focused on green tea consumption, likely because of the prevailing catechin content (particularly epigallocatechin gallate). While effective tea dose and duration are contentious, catechin content of ~600 mg per day has been associated with thermogenic effects via sympathetic nervous system activity. This likely equates to > 3 cups of hot tea per day, which may partly explain the higher dose requirements observed in the current study, particularly for older women. Although tea catechin consumption has been proposed to inhibit catechol-O-methyltransferase activity (30), leading to sustained catecholamine effects on lipolysis and hence enhanced substrate oxidation, this effect may be short-lived once catechins undergo glucuronidation (31). In animal models, longer-term use of tea catechins has been shown to increase mRNA expression for both lipolytic and β-oxidation enzymes in liver or adipose tissue (32) and fat oxidation enzymes (e.g., NRF-1, UCP3, PPAR-α) in skeletal muscle (33). However, evidence of upregulation of metabolic genes associated with enhanced fat oxidation in humans is currently lacking (30, 34), and further research investigating the impact of regular consumption of tea catechins on fat oxidation mechanisms is warranted.
However, it is important to recognize that the catechin content of tea has been shown to be variable (35), and it is influenced by factors including where the plant is grown (quality of soil, altitude), the specific season of harvest, and leaf age or storage. During the brewing process, water temperature has also been shown to affect polyphenol levels, with ideal temperatures > 80°C needed to improve catechin extraction (36). In addition, brewing times (37, 38) exceeding 4 minutes potentially lend to optimal polyphenol provision, which may be an important factor considering the bioavailability of tea catechins in vivo (39). This, in part, may explain the modest differences in total and trunk body fat observed in the current study and indeed the variability observed between participants. It is also important to note that in the current study, we did not differentiate between tea classifications (i.e., black, green, or yellow) to establish whether specific types of tea are more advantageous.
An interesting observation from the current study was that a higher dose of daily tea consumption in women was associated with reduced trunk body fat compared with men. This supports findings elsewhere (40) that BMI tended to be lower in women who consumed higher total flavonols or flavones and catechins in their diet in contrast to men. The lower tea dose observed in the current study for reduced total body fat and trunk fat for men may be particularly important considering the relevance of central adiposity (visceral adipogenesis) in the chronic development of cardiometabolic health disorders. Adipogenesis in women is typically associated with gynoid fat distribution, and reduction of central fat storage sites may require greater sympathetic nervous system stimulation (41).
It is important to note the observed lower level of body fat in this study associated with drinking hot tea. It was observed that men who reported consuming 0.25 to 1 cups of hot tea per day and women who consumed 1 or more cups of hot tea per day had significantly lower total body fat percentage than those who reported no hot tea consumption (1.5% and 0.8% lower, respectively). Although clinically significant weight loss has previously been defined as at least a 5% reduction in weight from the baseline level (42), any reduction in weight is likely to benefit health, and if further research confirms present findings, it is feasible that drinking hot tea could be used as an additional strategy, for example combined with exercise, to aid weight loss.
The inclusion of a large representative sample of US adults and the adjustment for a range of social and biological covariates are important design strengths to the current study. In addition, whereas previous research (12) has assessed the impact of hot tea consumption on body weight and selected skinfold measures, the inclusion of trunk fat derived from DXA scans provides important information pertinent to the estimation of central adiposity. However, it is also acknowledged that as a cross-sectional study, the direction of causality is not quantifiable, and it is therefore not possible to determine whether regular consumption of hot tea is directly or mechanistically causal in reducing total or central body fat or in limiting adipose storage. Furthermore, it is important to recognize that the assessment of trunk fat based on DXA analyses encompasses both visceral and subcutaneous adipose tissue as opposed to specific abdominal visceral tissue only. Further experimental research is therefore warranted to corroborate these findings, utilizing more robust measures such as magnetic resonance imaging or computed tomography to establish whether regular hot tea consumption specifically modulates abdominal visceral fat reduction.
Finally, another acknowledged limitation of the current study is the use of the FFQ to establish consumption levels. While these questionnaires are widely used in epidemiological research to practically collate population-specific intakes, these are nevertheless subject to methodological limitations, including quantity underestimation, individual recall bias, and interindividual variability pertinent to portion size or beverage volume. In addition, pending categories included in the FFQ and certain foods or classifications may be excluded. As such, the use of dietary estimated measures has been challenged, warranting caution when interpreting findings (43-45).
Conclusion
Daily consumption of hot tea is associated with lower total and trunk body fat percentage in both men and women. Multivariable-adjusted models, particularly taking into consideration ethnicity and coffee and iced tea consumption, indicate a potential dose response with women requiring more than 1 cup of hot tea per day to be associated with lower trunk body fat percentage compared with men. Therefore, further longitudinal studies are needed to investigate the potential of using hot tea as an important dietary strategy to reduce central adiposity among men.
