1. Dr. Connie Weaver Department of Nutrition Science Purdue University
Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children: Bone and Calcium Outcome
Dr. Connie Weaver
Department of Nutrition Science
Purdue University

2. Disclosure
Member of the ILSI North America Caffeine Systematic Review Team
Vice-Chair of ILSI Global Board of Trustees
Science Advisory Board of Pharmavite
Grant from Alliance of Potato Research and Education

3. PECO Questions for the Bone and Calcium Outcome
For [population], is caffeine intake above [dose], compared to intakes [dose] or less, associated with adverse effects on bone and calcium outcomes?
Population
Healthy
Adults
Pregnant Women
Healthy Adolescents
Children
Exposure
> 400 mg/day
> 300 mg/day
> 2.5 mg/kg-day
Comparator
≤ 400 mg/day
≤ 300 mg/day
≤ 2.5 mg/kg-day
Outcome
Adverse effects on bone and calcium
Example: For healthy adults, is caffeine intake above 400 mg/day, compared to intakes of 400 mg/day or less, associated with adverse effects on bone and calcium outcomes?

4. Caffeine

5. Characterization of Data for Bone and Calcium Outcome
Data Type
Characterization
Number of studies
14 included; 26 excluded
Study types
All observational (cohort and cross-sectional); exception of 2 RCTs for calcium homeostasis
Populations
Adult (women/men; elderly; 1 study that included adolescents)
Exposure
Primarily dietary intake (e.g., food frequency questionnaires) – coffee, soda, tea, chocolate
~1/2 specifically evaluated caffeine
Categorical groupings (e.g., <1 cup/day, >3 cups/day)
Outcome (Endpoints)
Risk of fracture (6)
Bone mineral density (BMD) and osteoporosis (9)
Calcium homeostasis (2)

6. Results: Risk of Fracture and Fall
Discuss importance of calcium?
Urinary calcium excretion is affected by calcium intake, so calcium intake needs to be considered in the analysis. Altered calcium balance through perturbing calcium excretion can influence bone mas
The majority, although not all, of the data demonstrate a lack of effects of caffeine consumption at levels both above (up to 760 mg/day) and below 400 mg/day
Effects <400 were of low magnitude (RR = <1.2) or were reported in analyses that did not consistently control for calcium intake
Moderate confidence: findings generally consistent, most studies controlled for calcium intake

7. Results: BMD and Osteoporosis
Discuss importance of calcium?
Urinary calcium excretion is affected by calcium intake, so calcium intake needs to be considered in the analysis. Altered calcium balance through perturbing calcium excretion can influence bone mas
The majority of studies support that the comparator of 400 mg/day in healthy adults is not harmful with respect to BMD and osteoporosis
More evidence is needed for effects of caffeine intake between 200 and 400mg/day
Effects <400 or >400 were associated with subgroups, single sites, and/or not associated with downstream events
Moderate to low confidence: findings inconsistent, methods for controlling for calcium intake uncertain

8. Evaluation of Individual Study Quality (Risk of Bias)
Overall “probably low” risk of bias across body of evidence
Limited by exposure characterization (Q3, Q11)
Consideration of calcium intake inconsistent (Q4)
+2: Definitely low
+1: Probably low
-1: Probably high
-2: Definitely high

9. Factors that increased or decreased confidence in the body of evidence by endpoint
No. of Studies
Initial Confidence Rating
Based on study type and study features (OHAT, 2015)
Overall RoB
Domain-based evaluation of risk of bias per the OHAT RoB tool (OHAT, 2015)
Indirectness
Was the study designed to evaluate the PECO?
Magnitude
Strength of effect (when effect observed below the comparator)
Confounding
Were plausible confounders that would change the observed effect accounted for?
Consistency
Were findings consistent in demonstrating effects or lack of effects at or below the comparator
Final Confidence Rating
What is the overall rating when factors that increase or decrease confidence were considered
Risk of fracture and fall 6
Moderate - ↓
↓ / -
↑ / -
BMD and osteoporosis 7
Moderate to low
↑ increased confidence no change to confidence ↓ decreased confidence

10. Developing Conclusions for the Outcome: Integration of Weight of Evidence Considerations

11. WoE Conclusion: Bone and Calcium Outcome
The comparator, 400 mg/day, was found to be an acceptable intake that is not associated with significant concern regarding overt, adverse effects on bone or calcium endpoints, particularly under conditions of adequate calcium intake.
Some effects below the comparator; limited to physiological effects following acute exposure (altered calcium homeostasis) and subgroups in analyses of clinical endpoints (including those with low calcium intake)
Effects generally low magnitude and/or were of overall low/negligible consequence to downstream events
Several studies also reported on a lack of effect on the clinical endpoints following chronic consumption below the comparator, as well as above the comparator
Moderate level of confidence evidence base
Key limitations: inability to fully accommodate calcium intake, high level of indirectness, uncertainty in exposure estimates
From manuscript:
When the weight of evidence was considered, the comparator, 400 mg/day, was found to be an acceptable intake that is not associated with significant concern regarding overt, adverse effects on bone or calcium endpoints, particularly under conditions of adequate calcium intake. Although effects were observed at exposures below the comparator they were often limited to physiological effects following acute exposure (altered calcium homeostasis), and subgroups in analyses of clinical endpoints, including those with low calcium intake. Such effects were generally of low magnitude, and/or were of overall low/negligible consequence to downstream events. Several studies also reported on a lack of effect on the clinical endpoints following chronic consumption below the comparator, as well as above the comparator. Based on the underlying study type (11 observational, 2 RCTs, 1 meta-analysis) that constitute this evidence base, there is a moderate level of confidence in the research, which supports this conclusion. Key limitations that precluded a higher level of confidence were the inability to fully accommodate for calcium intake, the high level of indirectness, as well as an uncertainty in exposure estimates

12. Future Research Needs Non-adult populations Role of calcium
Understanding physiology