For 50 years, eggs were treated like a cardiovascular threat. The 1960s dietary guidelines capped cholesterol intake at 300mg per day. Two eggs put you at the limit. The advice moved millions away from the food, and away from a nutrient profile we didn't fully appreciate at the time.
A new study from Loma Linda University followed 39,498 adults age 65 and older for 15.3 years. The team linked Adventist Health Study-2 dietary records with Medicare diagnoses. Over that window, 2,858 participants developed Alzheimer's disease.
The dose-response was clean.
Eating eggs 1 to 3 times a month: 17% lower incidence vs never-eaters.
2 to 4 per week: 20% lower.
5 or more per week, roughly one a day: 27% lower.
The mechanism story isn't new, but the cohort scale and 15-year follow-up are. Eggs are the densest natural source of choline in the American diet. One large egg supplies roughly 33% of the daily choline requirement. Choline is the substrate for acetylcholine, the neurotransmitter that drops in Alzheimer's. Donepezil, the most prescribed Alzheimer's drug, works by blocking acetylcholine breakdown. The disease is partly defined by cholinergic neuron loss.
Egg yolk also delivers lutein and zeaxanthin. These are the only two carotenoids that cross the blood-brain barrier and accumulate in cortical tissue. Higher tissue levels track with better processing speed and memory across multiple older-adult cohorts. Yolk also contains DHA, primarily in phospholipid form. Phospholipid DHA enters the brain more efficiently than DHA in triglyceride form, which is the dominant form in fish oil capsules.
Now the caveats, because they matter.
This is observational. Causation cannot be drawn from a cohort study. The Adventist Health Study-2 cohort skews heavily vegetarian and health-conscious, so people who eat eggs in this cohort do not look like the average American egg-eater. The "never eats eggs" comparison group is largely vegan, which is its own dietary pattern with its own complications. Reverse causation also has to be considered. People in early Alzheimer's often change eating patterns before diagnosis. Some of the apparent protection could be that healthier brains keep eating eggs, not the other way around.
The mechanism story I outlined above is supported by adjacent literature, not by this paper. The study did not measure choline status, lutein levels, or DHA in tissue. It measured eggs in, dementia out.
What we can say honestly: in a 40,000-person cohort followed for 15 years, egg intake tracked with substantially lower Alzheimer's incidence in a dose-response pattern. The mechanism is biochemically plausible, supported by other lines of evidence, and consistent with what we know about acetylcholine and brain carotenoid status. The randomized trial that would prove causation has not been run.
The practical version: if you are over 50 and not allergic, eating an egg most days has stronger evidence behind it for brain health than most products marketed for the same goal. Five days a week was the dose with the lowest risk in this cohort. Even 1 to 3 per month showed measurable benefit.
For 50 years the question was whether eggs were dangerous to your heart. The data behind that fear was always weaker than the guidelines made it sound, which is why the 2015 Dietary Guidelines for Americans quietly removed the 300mg cap. The brain question got asked too late.
Oh et al., J Nutr, 2026 (DOI: 10.1016/j.tjnut.2026.101541)