Are eggs bad for cholesterol? The cohorts disagree and the trial found nothing.

The best available evidence does not show that eating up to one egg a day raises cardiovascular risk in the general population, and the only randomised trial to test eggs directly in people at high cardiovascular risk found no meaningful change in LDL or HDL cholesterol over four months [s1] [s3]. It also does not show eggs are inert: a pooled analysis of six US cohorts found dietary cholesterol itself associated with higher risk in a dose-response pattern, and eggs are a major source of it [s2]. The two findings are not as contradictory as they look, and the reason why is the useful part.

The cohort that found nothing

Researchers followed 83,349 women in the Nurses' Health Study, 90,214 women in NHS II and 42,055 men in the Health Professionals' Follow-Up Study, all free of cardiovascular disease, type 2 diabetes and cancer at baseline [s1]. Over up to 32 years and more than 5.54 million person-years, 14,806 developed cardiovascular disease [s1]. Eating at least one egg a day, compared with fewer than one a month, carried a hazard ratio of 0.93 (95% confidence interval 0.82 to 1.05) once lifestyle and dietary factors associated with egg intake were accounted for [s1].

The authors then folded their cohorts into an updated meta-analysis: 33 risk estimates, 1,720,108 participants and 139,195 cardiovascular events [s1]. One additional egg per day carried a pooled relative risk of 0.98 (0.93 to 1.03) for cardiovascular disease, 0.96 (0.91 to 1.03) for coronary heart disease and 0.99 (0.91 to 1.07) for stroke [s1]. Geography mattered more than the egg did: no association in US cohorts (1.01, 0.96 to 1.06) or European ones (1.05, 0.92 to 1.19), but an inverse association in Asian cohorts (0.92, 0.85 to 0.99) [s1].

The cohort that found something

A year earlier, a pooled analysis of individual participant data from six US cohorts reached the opposite headline. Among 29,615 adults followed for a median of 17.5 years, with 5,400 cardiovascular events and 6,132 deaths, each additional 300 mg of dietary cholesterol per day was associated with higher risk of incident cardiovascular disease (hazard ratio 1.17, 1.09 to 1.26) and all-cause mortality (1.18, 1.10 to 1.26) [s2]. Each additional half-egg per day carried a hazard ratio of 1.06 (1.03 to 1.10) for cardiovascular disease and 1.08 (1.04 to 1.11) for death [s2].

The line that decides how to read that study is buried in its own results. Once the analysis adjusted for dietary cholesterol, the association between egg consumption and cardiovascular disease (0.99, 0.93 to 1.05) and mortality (1.03, 0.97 to 1.09) was no longer significant [s2]. The egg, in that dataset, was a marker for the cholesterol it carried rather than an independent risk factor — and cholesterol intake is itself entangled with the rest of the diet.

Both papers are observational. Neither can separate an egg from what is usually eaten beside it. The BMJ analysis reports that participants with higher egg intake had a higher body mass index, were less likely to be taking statins, and ate more red meat [s1].

The trial

PROSPERITY randomised 140 patients who had either had a prior cardiovascular event or carried at least two cardiovascular risk factors, in a two-by-two design testing fortified eggs against a non-egg-supplemented diet and time-restricted eating against usual care [s3]. Participants assigned to eggs were instructed to eat at least 12 fortified eggs a week, which were supplied to them [s3]. Median age was 66, 51% were women, 27% were Black and 24% had diabetes [s3].

Over four months, the difference in least-squares means from baseline showed no clinically relevant separation: HDL −0.64 mg/dL (95% CI −3.86 to 2.58) and LDL −3.14 mg/dL (−10.81 to 4.52) for fortified eggs versus the non-egg diet [s3]. The time-restricted-eating comparison was likewise flat (HDL 1.51 mg/dL, −1.65 to 4.68; LDL 1.17 mg/dL, −6.36 to 8.70) [s3]. In a prespecified subgroup of participants aged 65 and over, eggs showed a non-significant HDL increase and LDL decrease [s3].

What the trial cannot tell you

PROSPERITY is small — 140 people — and short. It measured blood lipids, not heart attacks. It used fortified eggs, not ordinary ones, and its comparator group was asked to restrict eggs rather than to eat none. Its own stated conclusion is defensive rather than promotional: the data did not demonstrate clinically relevant differences, providing evidence that adverse short-term lipid changes did not occur [s3]. That is a narrower claim than "eggs are good for you," and it is the claim the trial supports.

Where this leaves the question

The popular answer — eggs raise cholesterol and should be limited — is not supported by the largest pooled cohort evidence at intakes up to one a day [s1], and the one randomised test in a high-risk group found no short-term lipid harm [s3]. The popular counter-answer, that dietary cholesterol is irrelevant, is also stronger than the evidence: the JAMA pooled analysis found a monotonic dose-response association for dietary cholesterol itself, and that association survived adjustment for the egg [s2]. Neither the cohorts nor the trial address intakes well above one egg a day, and none of this evidence was generated in people with familial hypercholesterolaemia or established diabetes, where the relevant clinical guidance is separate.

This article is informational and is not medical advice. Decisions about dietary cholesterol in the context of an existing lipid disorder belong with a clinician.

Sources

• Egg consumption and risk of cardiovascular disease: three large prospective US cohort studies, systematic review, and updated meta-analysis — The BMJ, 2020-03-04
• Associations of Dietary Cholesterol or Egg Consumption With Incident Cardiovascular Disease and Mortality — JAMA, 2019-03-15
• Effects of fortified eggs and time-restricted eating on cardiometabolic health: the PROSPERITY trial — American Heart Journal, 2024-10-15