Abstract
Few studies have evaluated the relationship between changes in diet quality over time and the risk of death. We used Cox proportional-hazards models to calculate adjusted hazard ratios for total and cause-specific mortality among 47,994 women in the Nurses’ Health Study and 25,745 men in the Health Professionals Follow-up Study from 1998 through 2010. Changes in diet quality over the preceding 12 years (1986–1998) were assessed with the use of the Alternate Healthy Eating Index-2010 score, the Alternate Mediterranean Diet score, and the Dietary Approaches to Stop Hypertension (DASH) diet score. The pooled hazard ratios for all-cause mortality among participants who had the greatest improvement in diet quality (13 to 33% improvement), as compared with those who had a relatively stable diet quality (0 to 3% improvement), in the 12-year period were the following: 0.91 (95% confidence interval [CI], 0.85 to 0.97) according to changes in the Alternate Healthy Eating Index score, 0.84 (95% CI, 0.78 to 0.91) according to changes in the Alternate Mediterranean Diet score, and 0.89 (95% CI, 0.84 to 0.95) according to changes in the DASH score. A 20-percentile increase in diet scores (indicating an improved quality of diet) was significantly associated with a reduction in total mortality of 8 to 17% with the use of the three diet indexes and a 7 to 15% reduction in the risk of death from cardiovascular disease with the use of the Alternate Healthy Eating Index and Alternate Mediterranean Diet. Among participants who maintained a high-quality diet over a 12-year period, the risk of death from any cause was significantly lower — by 14% (95% CI, 8 to 19) when assessed with the Alternate Healthy Eating Index score, 11% (95% CI, 5 to 18) when assessed with the Alternate Mediterranean Diet score, and 9% (95% CI, 2 to 15) when assessed with the DASH score — than the risk among participants with consistently low diet scores over time. Improved diet quality over 12 years was consistently associated with a decreased risk of death. (Funded by the National Institutes of Health.)
Generated Summary
This research, published in the New England Journal of Medicine, presents a prospective study evaluating the relationship between changes in diet quality and mortality risk over time. The study utilized data from the Nurses’ Health Study and the Health Professionals Follow-up Study, encompassing 47,994 women and 25,745 men. Participants’ dietary patterns were assessed using the Alternate Healthy Eating Index-2010 score, the Alternate Mediterranean Diet score, and the Dietary Approaches to Stop Hypertension (DASH) diet score. The primary aim was to determine how changes in these diet-quality scores over a 12-year period (1986-1998) correlated with total and cause-specific mortality from 1998 through 2010. The study employed Cox proportional-hazards models to calculate adjusted hazard ratios. Furthermore, the study examined shorter-term (baseline to 8-year follow-up) and longer-term (baseline to 16-year follow-up) changes in diet quality in relation to mortality, providing a comprehensive analysis of the impact of dietary changes on health outcomes. The study’s methodology involved detailed dietary assessments using validated food frequency questionnaires, assessing lifestyle factors, and gathering information on deaths. The statistical analyses included categorization of diet-quality scores into quintiles and the use of multivariable models to estimate hazard ratios, accounting for potential confounders. The study underscores the importance of assessing dietary changes and their impact on health outcomes over time.
Key Findings & Statistics
- The study found that the greatest improvement in diet quality (13 to 33% improvement), as compared with those who had a relatively stable diet quality (0 to 3% improvement), resulted in the following hazard ratios for all-cause mortality: 0.91 (95% CI, 0.85 to 0.97) for the Alternate Healthy Eating Index score, 0.84 (95% CI, 0.78 to 0.91) for the Alternate Mediterranean Diet score, and 0.89 (95% CI, 0.84 to 0.95) for the DASH score.
- A 20-percentile increase in diet scores was significantly associated with a reduction in total mortality: 8 to 17% with the use of the three diet indexes.
- A 20-percentile increase in diet scores was significantly associated with a 7 to 15% reduction in the risk of death from cardiovascular disease with the use of the Alternate Healthy Eating Index and Alternate Mediterranean Diet.
- Among participants who maintained a high-quality diet over a 12-year period, the risk of death from any cause was significantly lower: by 14% (95% CI, 8 to 19) when assessed with the Alternate Healthy Eating Index score, 11% (95% CI, 5 to 18) when assessed with the Alternate Mediterranean Diet score, and 9% (95% CI, 2 to 15) when assessed with the DASH score, than the risk among participants with consistently low diet scores over time.
- In the Nurses’ Health Study, 5967 deaths were documented, including 1115 deaths from cardiovascular disease and 2089 deaths from cancer.
- In the Health Professionals Follow-up Study, 3979 deaths were documented, including 1226 deaths from cardiovascular disease and 1192 deaths from cancer.
- The pooled hazard ratios among participants with the greatest improvement in diet quality (13 to 33% improvement) were: 0.91 (95% CI, 0.85 to 0.97) for the Alternate Healthy Eating Index score; 0.84 (95% CI, 0.78 to 0.91) for the Alternate Mediterranean Diet score; and 0.89 (95% CI, 0.84 to 0.95) for the DASH score.
- A decrease in diet quality, compared with no change, was associated with increased total mortality: hazard ratio, 1.12 (95% CI, 1.05 to 1.19) for the Alternate Healthy Eating Index score; 1.06 (95% CI, 0.99 to 1.13) for the Alternate Mediterranean Diet score; and 1.06 (95% CI, 1.00 to 1.12) for the DASH score.
- A 20-percentile increase in diet-quality scores was associated with a reduction of 8 to 17% in the risk of death from any cause.
- A 20-percentile increase in the Alternate Healthy Eating Index and Alternate Mediterranean Diet scores was associated with a significantly reduced risk of death from cardiovascular disease (pooled hazard ratio, 0.85; 95% CI, 0.76 to 0.96, and 0.93; 95% CI, 0.88 to 0.99 respectively)
- A 20-percentile increase in the DASH score was associated with a significantly reduced risk of death from cancer (0.91; 95% CI, 0.84 to 0.98).
- The greatest improvement in diet quality over 12 years: had a 15% (95% CI, 3 to 25) lower risk of death from any cause when diet quality was assessed with the Alternate Healthy Eating Index score; 23% (95% CI, 12 to 32) with the Alternate Mediterranean Diet score; and 28% (95% CI, 16 to 38) with the DASH score.
- Those who had consistently high diet scores over time had a 14% (95% CI, 8 to 19) lower risk of death from any cause according to the Alternate Healthy Eating Index score, 11% (95% CI, 5 to 18) according to the Alternate Mediterranean Diet score, and 9% (95% CI, 2 to 15) according to the DASH score.
- A 20-percentile increase in any of the three diet scores during the first 8, 12, and 16 years was significantly associated with a reduced risk of death from any cause.
- A 20-percentile increase in the Alternate Healthy Eating Index score over 8 years was associated with a reduction in mortality of 11% (95% CI, 6 to 15), whereas among participants with the same degree of improvement over 16 years, the reduction in mortality was 26% (95% CI, 21 to 31).
Other Important Findings
- Participants with a greater increase in diet quality were younger, engaged in more physical activity, and consumed less alcohol.
- Participants with consistently high diet quality at baseline and 12 years later were older, had a lower BMI, and were less likely to be current smokers.
- Participants with a greater increase in diet quality reported increased consumption of whole grains, vegetables, and n−3 fatty acids, and decreased sodium intake over time.
- Similar patterns were observed with assessments based on the Alternate Mediterranean Diet and DASH scores.
- Improvement in the Alternate Healthy Eating Index score over a 12-year period could reduce risk of death by nearly 20% in the subsequent 12 years.
- Increased consumption of nuts and legumes from no servings to 1 serving per day and a reduction in consumption of red and processed meats from 1.5 servings per day to little consumption will result in an improvement of 20 points in the score.
- The inverse association between higher scores in the Alternate Healthy Eating Index or the Mediterranean-style diet and a lower risk of death from cardiovascular disease.
Limitations Noted in the Document
- Dietary data were self-reported, leading to potential measurement errors.
- Residual and unmeasured confounding could not be completely ruled out.
- The study did not examine the association of each component of the scores and mortality.
- Generalizability may be limited as participants were mostly white health professionals.
Conclusion
The findings from this study strongly support the benefits of improving diet quality over time, as assessed by multiple dietary indexes. The significant inverse associations between changes in diet-quality scores and both total and cause-specific mortality provide compelling evidence for the positive impact of dietary improvements. As stated in the article, ‘Improved diet quality over 12 years was consistently associated with a decreased risk of death.’ A key takeaway is that even moderate improvements in dietary habits can lead to meaningful reductions in mortality risk. The results underscore the importance of adhering to dietary recommendations, such as those outlined in the 2015 Dietary Guidelines, which advocate for the Alternate Healthy Eating Index, Alternate Mediterranean Diet, and DASH diet as viable and beneficial eating plans. The study also highlighted the role of specific dietary components, such as whole grains, vegetables, fruits, and fish or n−3 fatty acids, in promoting health. The study’s finding that changes in diet quality were associated with a reduced risk of death from cardiovascular disease and from any cause underscores the importance of dietary changes over the long term. This supports the concept that the dietary improvements can lower the risk of various diseases. Furthermore, as the authors state, ‘These results underscore the concept that moderate improvements in diet quality over time could meaningfully decrease the risk of death.’ The consistent findings across different diet-quality scores provide strong support for dietary guidelines that encourage balanced eating patterns. The study’s emphasis on the dose-dependent nature of the relationship between diet quality and mortality highlights the importance of continuous efforts to improve dietary habits for long-term health benefits.