Abstract
The geroscience hypothesis proposes that therapy to slow or reverse molecular changes that occur with aging can delay or prevent multiple chronic diseases and extend healthy lifespan1–3. Caloric restriction (CR), defined as lessening caloric intake without depriving essential nutrients1, results in changes in molecular processes that have been associated with aging, including DNA methylation (DNAm)5–7, and is established to increase healthy lifespan in multiple species8. Here we report the results of a post hoc analysis of the influence of CR on DNAm measures of aging in blood samples from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) trial, a randomized controlled trial in which n = 220 adults without obesity were randomized to 25% CR or ad libitum control diet for 2 yr (ref. 10). We found that CALERIE intervention slowed the pace of aging, as measured by the DunedinPACE DNAm algorithm, but did not lead to significant changes in biological age estimates measured by various DNAm clocks including PhenoAge and GrimAge. Treatment effect sizes were small. Nevertheless, modest slowing of the pace of aging can have profound effects on population health11–13. The finding that CR modified DunedinPACE in a randomized controlled trial supports the geroscience hypothesis, building on evidence from small and uncontrolled studies14–16 and contrasting with reports that biological aging may not be modifiable17. Ultimately, a conclusive test of the geroscience hypothesis will require trials with long-term follow-up to establish effects of intervention on primary healthy-aging endpoints, including incidence of chronic disease and mortality18–20.
Generated Summary
This research investigates the impact of long-term caloric restriction (CR) on DNA methylation (DNAm) measures of biological aging in healthy adults. The study used data from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) trial, a randomized controlled trial involving 220 adults without obesity. The primary goal was to determine if CR, defined as reducing caloric intake, influences DNAm patterns associated with aging. The study focused on blood samples and measured biological aging using the DunedinPACE DNAm algorithm, along with PhenoAge and GrimAge, which are DNAm clocks. The study employed a post hoc analysis design, examining the influence of CR on these aging measures. Participants were randomly assigned to either a 25% CR diet or an ad libitum control diet for two years. The research aimed to test the geroscience hypothesis, which posits that interventions can slow or reverse molecular changes associated with aging, thereby delaying or preventing chronic diseases and extending lifespan. The primary analysis compared change scores of aging measures between the CR and control groups using repeated-measures analysis of covariance (ANCOVA) under mixed models. Additionally, the study conducted intent-to-treat (ITT) analysis to assess the effects of CR and also explored dose-response relationships and the effect of CR on participants who achieved a higher level of CR.
Key Findings & Statistics
- The CALERIE trial enrolled 220 adults; 145 in the CR group and 75 in the AL control group.
- DNAm data were available for 197 participants: 128 in the CR group and 69 in the AL group.
- Participants had a mean age of 38 years (SD = 7).
- 70% of participants were women, and 77% were white.
- The study used the Illumina Infinium Methylation EPIC BeadChip arrays to quantify DNAm.
- Participants were randomly assigned at a ratio of 2:1 to a CR behavioral intervention or an ad libitum (AL) control group.
- The precise level of CR achieved was quantified by comparing energy intake (determined periodically throughout the trial by the DLW method) during the CR intervention with baseline energy intake.
- At baseline, the average energy intake in the CR group was 2,124 kcal/day (SD = 558), and in the AL group, it was 2,045 kcal/day (SD = 481).
- The analysis sample consisted of participants with DNAm data available at baseline and at least one follow-up assessment.
- The study used P < 0.005 as a conservative threshold for statistical significance.
- For the PhenoAge, and GrimAge clocks, change score values were scaled by the standard deviation of the difference between clock age and chronological age at pretreatment baseline.
- For DunedinPACE, change score values were scaled by the standard deviation at pretreatment baseline.
- The study found that CALERIE intervention reduced participants’ DunedinPACE by the 12-month follow-up. (12-month d = -0.29 (95% CI -0.45, -0.13), 24-month d = -0.25 (95% CI -0.41, -0.09), P < 0.003 for both).
- The treatment effect on DunedinPACE corresponds to a reduction in the pace of aging of 2-3%.
- In the >10% CR group, the treatment effect for DunedinPACE was d = -0.33 at 12 and 24 months, compared to d = -0.19 at 12 months and d = -0.14 at 24 months in the <10% CR group.
- For PhenoAge, 12-month d = -0.03 (95% confidence interval (95% CI) -0.19, 0.12), 24-month d = 0.05 (95% CI -0.11, 0.20), P>0.50 for both.
- For GrimAge, 12-month d = -0.04 (95% CI -0.16, 0.07), 24-month d = 0.05 (95% CI -0.07, 0.17), P> 0.40 for both.
- The effect of 20% CR on DunedinPACE was d = -0.43 (95% CI -0.67, -0.19) at 12 months and d = -0.40 (95% CI -0.67, -0.12) at 24 months (P < 0.005 for both).
- IV effect-size estimates for PhenoAge and GrimAge were small (d = -0.13-0.01; P > 0.15).
Other Important Findings
- The study’s main finding was that the CALERIE intervention slowed the pace of aging as measured by the DunedinPACE DNAm algorithm, but did not lead to significant changes in biological age estimates measured by PhenoAge and GrimAge.
- The study highlights that modest slowing of the pace of aging can have profound effects on population health.
- The finding that CR modified DunedinPACE in a randomized controlled trial supports the geroscience hypothesis.
- The research indicates that treatment effect sizes were small.
- The study found that participants’ PhenoAge and GrimAge values tended to increase over time.
- Change in PhenoAge and GrimAge values did not differ between CR and AL groups.
- In the CALERIE trial, the %CR achieved by participants in the treatment group varied.
- In the CALERIE Trial, the %CR achieved by participants in the treatment group varied.
- Standardized treatment effects on DunedinPACE correspond to a reduction in the pace of aging of 2-3%.
- There was no evidence of a dose-response effect for PhenoAge or GrimAge.
- CR effects varied across the DNAm measures of aging.
- CALERIE intervention slowed the pace of aging as measured by DunedinPACE, whereas the CR intervention did not affect the PhenoAge and GrimAge DNAm clocks.
- The findings indicate DunedinPACE may be helpful in identifying short-term interventions worthy of long-term follow-up to generate such evidence.
Limitations Noted in the Document
- The study acknowledges the absence of a gold standard measure for biological aging.
- The DNAm measures used have limitations and are acknowledged to be incomplete summaries of biological changes.
- Treatment effects on aspects of biological aging not captured by the DNAm measures are not included in effect estimates.
- Measurement error due to technical limitations of DNAm assays may bias effect estimates towards the null.
- The measures used summarize biological aging in general and do not isolate system-specific aging processes.
- Trial participants did not achieve the prescribed 25% CR, and some control group participants reduced caloric intake.
- The CALERIE Trial sample may not represent the general population, and treatment effects might not generalize beyond the healthy volunteers.
- CALERIE follow-up is limited to the intervention period.
Conclusion
The study’s findings support the geroscience hypothesis by demonstrating that long-term caloric restriction can influence the pace of biological aging, as measured by the DunedinPACE DNAm algorithm. The results, while showing modest effects, provide a foundation for future geroscience research. The impact of CR on DunedinPACE suggests a potential for this measure in identifying short-term interventions that warrant long-term follow-up. The study underscores the need for trials with extended follow-up to determine the long-term clinical benefits of CR, including its effects on chronic disease and mortality. In the context of the limitations, the findings highlight DunedinPACE as a potentially useful measure in future trials, with its reliability and association with healthspan endpoints. Further research should focus on the long-term impacts of the interventions on primary aging-related outcomes. The study’s insights can guide policy makers in forecasting the potential benefits of interventions designed to delay aging, assuming modest intervention effects. The authors emphasize the need for more trials with larger samples and, potentially, less intensive interventions, to confirm the effects and assess the potential for translating these findings into tangible health benefits. The variability in the CR achieved by participants underscores the importance of dose-response analysis and suggests that future studies may benefit from focusing on interventions that are more readily achievable in real-world settings. This research contributes to the growing body of evidence on the role of interventions in modifying the aging process and has implications for both research and public health efforts aimed at extending healthspan.