Longitudinal Association of Coffee and Tea Consumption with Bone Mineral Density in Older Women: A 10-Year Repeated-Measures Analysis in the Study of Osteoporotic Fractures

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https://www.mdpi.com/2072-6643/17/23/3660

Gemini picked up my issue which is that an 0.3% increase in bone density is neither here nor there.

Gemini:

Here is the summary, assessment of novelty, and critique of the paper “Longitudinal Association of Coffee and Tea Consumption with Bone Mineral Density in Older Women: A 10-Year Repeated-Measures Analysis in the Study of Osteoporotic Fractures”.

1. Summary of the Study

Objective The study aimed to evaluate the longitudinal associations between coffee and tea consumption and Bone Mineral Density (BMD) in postmenopausal women. While previous research has been inconclusive, this study sought to clarify these relationships using repeated measurements over an extended follow-up period.

Methodology

  • Cohort: Data were drawn from the Study of Osteoporotic Fractures (SOF), a prospective cohort of 9,704 women aged $\ge65$ years.
  • Timeline: Participants were assessed at visits 2, 4, 5, and 6, spanning approximately 10 years.
  • Measurements:
    • Exposure: Coffee and tea intake were assessed via self-administered questionnaires at each visit.
    • Outcome: Femoral neck and total hip BMD were measured using dual-energy X-ray absorptiometry (DXA). * Statistical Analysis: Linear mixed-effects models were used to estimate associations, adjusting for covariates such as demographics, BMI, smoking, and alcohol use. Nonlinear relationships were assessed using natural splines.

Key Findings

  • Tea Consumption: Tea intake was positively associated with total hip BMD. The least squares mean for tea drinkers was $0.718~g/cm^{2}$ compared to $0.715~g/cm^{2}$ for non-drinkers (mean difference: 0.003; 95% CI: 0.000–0.005; $p=0.026$).
  • Coffee Consumption: There was no significant overall association between coffee consumption and femoral neck or total hip BMD. However, spline analyses suggested that consuming $>5$ cups of coffee per day may be associated with lower BMD.
  • Interactions:
    • Coffee & Alcohol: Coffee consumption was negatively associated with femoral neck BMD specifically in women with higher alcohol intake ($p=0.0147$).
    • Tea & BMI: Tea consumption appeared particularly beneficial for women with obesity ($p=0.0175$).

2. Novelty of the Research

This study distinguishes itself from prior literature in three specific ways:

  1. Repeated Measures Design: Unlike prior studies that often relied on baseline data or single-point measurements, this study utilized repeated measures of both beverage intake and BMD over a 10-year period. This allows for a more accurate reflection of real-world changes in consumption habits and bone health over time.
  2. Specific Subgroup Interactions: The study identified novel interaction effects that provide a more nuanced view of the risks. It highlighted that the detrimental effects of coffee are modified by alcohol intake, and the protective effects of tea are modified by BMI (specifically benefiting those with obesity).
  3. Non-Linear Dose Response: The application of natural spline regression revealed a potential threshold effect for coffee, suggesting that while moderate consumption (2–3 cups) is neutral, excessive consumption (>5 cups) poses a risk.

3. Critique of the Paper

Strengths

  • Robust Analytic Framework: The use of linear mixed-effects models with random intercepts is a significant strength. This statistical approach effectively handles time-dependent covariates and missing data under the Missing at Random (MAR) assumption.
  • Large Sample and Duration: The study leveraged a large, well-characterized cohort ($N=9704$ at start; 24,638 total observations analyzed) with a long follow-up duration, which minimizes measurement error compared to smaller, cross-sectional studies.
  • Comprehensive Covariate Adjustment: The analysis adjusted for a wide range of confounders, including lifetime physical activity, medication use (estrogen/steroids), and comorbidities, increasing the reliability of the associations.

Limitations

  • Generalizability: The study population consisted almost entirely of White older women in the United States. As BMD and dietary patterns vary significantly across racial and ethnic groups, the findings may not apply to broader populations.
  • Clinical Significance vs. Statistical Significance: While the positive association between tea and BMD was statistically significant, the mean difference ($\approx 0.003~g/cm^{2}$) is small and falls below the threshold typically considered clinically meaningful for individual patient management.
  • Measurement Error: Consumption data relied on self-reports without details on cup size, brew strength, or specific types of tea/coffee, which may introduce measurement and recall bias.
  • Attrition Bias: Due to the advanced age of the cohort (mean age rising from 73 to 80), there was a high rate of mortality and exclusion due to missing BMD data, which might introduce bias despite the statistical methods used.

Next Step:

Would you like me to extract the specific statistical data regarding the interaction between alcohol intake and coffee consumption to better understand the risk profile for that subgroup?

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