No study, from Harvard or anywhere else, has found that eating eggs adds 10 years to life. After multiple search strategies, no source attributing a 10-year lifespan gain to eggs or an "egg diet" could be located.

The 10-year figure that does exist in the nutrition literature comes from a completely different study. Fadnes et al. (PLOS Medicine, 2022), from the University of Bergen in Norway, modeled the effect of shifting from a typical Western diet to an "optimized" dietary pattern. A young adult in the U.S. could add more than a decade to life expectancy by moving to a diet with more legumes, whole grains and nuts, and less red and processed meat. The modeled gain was roughly 10 years for a young adult and about 6 to 7 years for a middle-aged adult. Eggs were a minor and largely neutral component of that model, with the optimal intake set at roughly 25 g per day, about half an egg. The authors themselves flagged that the evidence quality for eggs and white meat was lower than for whole grains, fish, processed meat and nuts.

On eggs specifically, the actual evidence is mixed and modest in both directions:

• The 2025 Australian ASPREE cohort (8,756 adults aged 70+, Monash University, not Harvard) found that people eating eggs 1 to 6 times per week had roughly a 15% lower risk of all-cause mortality (HR 0.85, 95% CI 0.74 to 0.98) and a 29% lower risk of cardiovascular death (HR 0.71, 95% CI 0.54 to 0.91) compared with those who rarely or never ate eggs. This is a relative risk reduction in one older population, not a lifespan extension figure, and it is not from Harvard.
• The 2022 Circulation study and meta-analysis analyzed 27,078 men in the Finnish ATBC cohort over 31 years plus pooled data from 41 cohort studies, and found that egg consumption of about one per day and higher dietary cholesterol were associated with a slightly higher risk of overall and cardiovascular mortality, with a positive association in U.S. cohorts and no association in Asian cohorts.
• The 2019 JAMA study, summarized by Harvard's own Nutrition Source, found that each additional half egg per day was associated with 6% higher CVD risk and 8% higher all-cause mortality risk. Harvard nutrition researcher Walter Willett publicly criticized that study's methodology, noting it measured diet only once.

What Harvard actually says: Harvard Health's position is essentially neutral-to-permissive, not enthusiastic. Its guidance is that the evidence does not support banning eggs, that people should focus on overall diet and exercise, and that an average of one egg a day can be part of a healthy lifestyle. Large studies have not found higher rates of heart attack or stroke in people eating up to one egg per day, but Harvard also notes exceptions for people with heart disease or diabetes. Nowhere does Harvard state that eggs extend life, and its 2022 coverage of the Circulation study was headlined around the question of whether an egg a day is really okay.