In a recent study published in Frontiers in Nutrition, researchers assessed the causal relationship between tea consumption and total-body (TB) bone mineral density (BMD).
Study: Tea intake and total body bone mineral density of all ages: a Mendelian randomization analysis. Image Credit: Wiro.Klyngz/Shutterstock.com
Background
BMD is an indicator of bone strength and a crucial measure of osteoporosis examination. Osteoporosis risk has been increasing with the aging global population, and it represents a significant public health concern.
Osteoporosis strongly correlates with age and gender, influenced by body mass index (BMI), race, lifestyle choices, and height.
The relationship between BMD and tea intake has been debatable. Previously, it was considered that tea consumption may result in calcium loss, contributing to osteoporosis; this stemmed from the notion that caffeine present in tea may impair calcium absorption and elevate its elimination through urine. However, tea composition is more complex than coffee, and its effects on bone density may vary.
By contrast, increasing evidence from observational studies indicates that tea intake does not contribute to calcium loss and bone density reduction.
Numerous studies have underscored the benefits of tea in bone density improvement and osteoporosis prevention.
Nevertheless, establishing conclusive evidence from observational research is challenging, and the causal link between tea and bone density remains undetermined.
About the study
The present study examined the causal relationship between tea consumption and TB-BMD using Mendelian randomization (MR) analysis. Data were obtained from reliable sources based on comprehensive genome-wide association studies (GWASs).
In particular, summary data on tea consumption and TB-BMD were obtained from the Integrative Epidemiology Unit (IEU) OpenGWAS project.
Tea intake data were secured from the United Kingdom (UK) Biobank. The Medical Research Council (MRC) IEU obtained data on herbal and green tea consumption.
TB-BMD dataset was obtained from a meta-analysis of 30 GWASs with > 56,000 individuals. BMD t-scores were used to identify individuals with osteoporosis or osteopenia, per the World Health Organization (WHO) criteria.
Instrumental variables (IVs) were single nucleotide polymorphisms (SNPs) associated with tea consumption at genome-wide significance. The PhenoScanner database was utilized to identify genetic variants associated with potential confounders.
Outcome data related to retained SNPs were extracted. Datasets were harmonized by excluding ambiguous and palindromic SNPs with non-concordant alleles to ensure consistency between exposure and outcomes.
A two-sample MR analysis assessed the causal association between genetically predicted tea consumption and TB-BMD, using methods like MR-Egger, simple or weighted mode, inverse-variance weighted (IVW), and weighted median.
Pleiotropy effects were identified/addressed using MR-regression and MR-pleiotropy residual sum and outlier (PRESSO) methods. A leave-one-out sensitivity analysis examined how individual SNPs impact the overall causal effect.
Findings
Overall, 41 SNPs were retained as IVs for tea consumption following the exclusion of SNPs with linkage disequilibrium.
The primary analytical method, IVW, showed a causal association between genetically predicted tea consumption and TB-BMD, particularly in the 45–60 age group.
However, this was not observed in other age groups (people aged ≤45 or ≥ 60). Other methods (simple or weighted mode, weighted median, and MR-Egger) showed concordant outcomes.
There was no significant heterogeneity between TB-BMD and tea intake; the lack of heterogeneity was consistent in the 45–60 age group. There was no evidence of directional pleiotropy, including in the 45–60 age group.
The sensitivity analysis revealed that the observed causal relationship was not driven by any individual SNP. Finally, there was no causal relationship between herbal or green tea intake and TB-BMD.
Conclusions
To summarize, the research team performed an MR analysis to investigate the causal effects of tea consumption on BMD.
The findings suggest that people with a greater genetic predisposition to consume increased quantities of tea were likelier to have higher BMD. Notably, the study exclusively included individuals of European ancestry, and MR outcomes vary by ethnicity.
Further, MR analyses cannot exhaustively rule out unknown/hidden confounders and only provide statistical evidence. Together, the results illustrate that a genetic predisposition to tea consumption was associated with improved BMD.
As such, moderate tea consumption may not warrant concerns about calcium loss or osteoporosis. Future studies with larger samples must corroborate the causal relationship and explore the underlying biological mechanisms.
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