Yerba mate is a xanthine-containing beverage that is popular in South America. It may be prepared as an infusion of dried leaves steeped in hot water and then filtered. More commonly, it is consumed through a metal straw inserted into a dried gourd containing the leaves, over which hot water is poured repeatedly, and it was these users who were included in the study. By this method, the tea contains caffeine at a concentration of about 330 mg/L.
In this cross-sectional, observational study, investigators identified postmenopausal women in the osteoporosis program who drank at least 1 L of yerba mate tea daily for at least 5 years (n = 146) and matched them by age and time since menopause with an equal number of women who did not drink yerba mate tea. Both groups were fairly sedentary, defined as not being in a program of physical exercise.
The 2 groups were well matched for age, time since menopause, height, body mass, and calcium intake. However, the tea drinkers had a body mass index 1.1 kg/m2 greater than the nondrinkers.
Current or former cigarette smokers, women who consumed more than 50 g of alcohol per week, those currently receiving hormone replacement therapy, those who had received bisphosphonate treatment for more than 6 months, or those who received chronic corticosteroid treatment were excluded.
One of the investigators, who was blinded to the yerba mate drinking status of each participant, performed the analysis of all the BMD measurements.
Measuring BMD by dual-energy X-ray absorptiometry (DXA), the researchers found that the tea drinkers had 9.7% greater lumbar spine BMD compared with non–tea drinkers (0.952 g/cm2 vs 0.858 g/cm2, respectively; P < .0001), as well as 6.2% greater femoral neck BMD (0.817 g/cm2 vs 0.776 g/cm2, respectively; P = .0002). By a multiple regression analysis, the researchers found that in addition to body mass index, drinking yerba mate tea was the only variable that significantly correlated with BMD at these sites (P = .0028).
Although the yerba mate group had higher lumbar spine and femoral neck BMD at all ages compared with control patients, the slopes of the regression lines for BMD vs age did not differ between the groups, indicating that loss of BMD over time was similar for the tea-drinkers and the control participants.
At the time of DXA scanning, the number of low-impact bone fractures was similar between the groups (13 for tea drinkers and 17 for control patients; P = .5637).
The authors conclude that chronic consumption of yerba mate tea was associated with greater BMD at the lumbar spine and femoral neck, "suggesting a protective effect of this tea on bone mass of postmenopausal women." They also note that their earlier hypothesis that yerba mate consumption, based on other investigators' reports of a deleterious effect of caffeine on BMD, "should be rejected."
Limitations of the study are its retrospective nature, participants' self-reports of yerba mate consumption, and that the study participants were a selected population of postmenopausal women in a program for the prevention, diagnosis, and treatment of osteoporosis. Results may not be generalizable to younger women, men, or children.
The study was supported by Obra Social de Empleados Públicos, Mendoza, Argentina. The authors have disclosed no relevant financial relationships.
Source: http://www.medscape.com/viewarticle/756242?sssdmh=dm1.747366&src=nldne
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