Warning for supplement-popping gym goers over kidney and liver concerns

By Nikki Hancocks

- Last updated on GMT

Getty | Nikolas
Getty | Nikolas

Related tags Research Sports nutrition liver function kidney function

New research has warned about the importance of expert guidance and biochemical monitoring for sports nutrition users, as it finds a link between supplement consumption and alterations in liver and kidney function.

Brazil has the second highest number of gyms, totalling more than nine million gym users in the country​ and this popularity has also increased the use of dietary supplements. However, the authors of the current study argue gyms promote the consumption of dietary supplements, culminating in the potential unnecessary consumption of these substances.

They say this paired with a lack of guidance and monitoring for the dietary supplements use can result in an abusive consumption​, raising concerns about safety, especially regarding kidney​ and liver function​. Studies into this potential link have thus far led to contradictory results.

The current cross-sectional study, from researchers at University of Santa Cruz do Sul, Brazil, aimed to examine the association between dietary supplements intake with alterations in the liver and kidney function markers among gym users.

The study

The participants of this study were gym users of 31 gyms from the municipality of Santa Cruz do Sul, in Rio Grande do Sul, Brazil. The gym users were invited to answer an online questionnaire about dietary supplementation and to perform biochemical tests by peers and friends at gyms, via emails, and social media.

The questionnaire contained closed and open questions divided into 3 sections: 1) sociodemographic characteristics: age, sex, and educational level; 2) training habits: time of exercise, physical exercise intensity, type of physical exercise, extra activities performed; 3) supplement use: supplement usage, duration of supplement intake, number of dietary supplements used, who provided supplement prescription, type of dietary supplements used, reasons for supplement use.

Body mass index (BMI) and fat percentage were also assessed using a full body sensor scale.

Of the total number of gym users (n=594, 266 male and 328 female, average age of 37±14 years), a subset (n=242, 114 male and 128 female) also gave blood samples. Blood collection and anthropometry was performed in the Laboratory of Biochemical of Exercise located at University of Santa Cruz do Sul, Brazil. Blood samples were drawn by a specialized professional, in the morning and after a 10-12h fasting period.

The liver function (hepatic function) markers analysed were the enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST, which can be released into the bloodstream when liver cells become damaged), alkaline phosphatase (AKP) and gamma-glutamyltransferase (Gama-GT). The kidney function (renal function) markers analysed were creatinine and urea (essential for the removal of residual nitrogen, caused by protein and amino acid metabolism).


Dietary supplements were consumed by 36.0% of the gym users. Men presented the highest dietary supplement usage (42.5%) and 8.3% reported consuming up to 5 types of supplements.

The resulting data revealed that individuals who took dietary supplements showed a higher prevalence of slight alterations in the AST enzyme after adjustments for sex and age OR=2.57; 95% CI=1.09-6.07). Similarly, gym users that consumed dietary supplements showed a higher chance for slight alterations in the urea.

The team could not find an association between the number of supplements taken and the liver and renal function markers.

Other hepatic function markers, and the creatinine marker were not associated with supplement intake.

However, the researchers note these results should be interpreted with caution. They did not evaluate diet intake, specific supplements, dose supplemented, or the use of others anabolicandrogenic steroids. The data are observational and so they cannot exclude the possibility that other factors may have contributed to the results. Secondly, the sample size may be also a limitation once there were sample losses due to the low adherence of participants to perform biochemical tests (loss of 40%). In addition, the occurrence of changes in liver and kidney markers is low in individuals who practice physical exercise and use supplements, requiring a larger sample size to significantly detect changes in these markers.

Thirdly, this study is composed of individuals who were undergoing moderate and intense resistance training. Therefore, these findings cannot be generalised to non-exercising/sedentary subjects, individuals in aerobic exercise training, or other populations not examined in this study.

Future studies should further explain the mechanisms related among dietary supplement intake and renal/hepatic alteration function.

The report concludes: "Our results showed that gym users who intake dietary supplements showed a higher chance to present slight alterations in the AST enzyme, and in urea. These data may contribute to the analysis of future studies, and be an alert for health professionals to outline goals and strategies that will contribute to the disease prevention and health promotion in this population.

"Although our findings have shown slight alterations in renal and hepatic markers, these results are not indicative of renal and hepatic damage; however, they indicate the need for biochemical monitoring of these markers to avoid possible alterations that could compromise the health of these individuals."

Source: British Journal of Nutrition

Schlickmann, D., Molz, P., Brand, C., Dos Santos, C., Da Silva, T., Rieger, A., and Franke, S.

"Liver and kidney function markers among gym users: the role of dietary supplement usage"