by Jack Norris, RD
There has been no prospective data on cognition in a cohort that includes a sizable number of vegans. Until now. Maybe.
The Chinese Longitudinal Healthy Longevity Survey (CLHLS) tests cognition every 2–3 years. They deliberately recruit very old adults. Field teams identify centenarians first, then enroll nearby 90–99 year-olds and 80–89 year-olds; they also include 65–79 year-olds (Zeng, 2017). This design intentionally creates a large pool of very old participants.
In January, researchers released a report analyzing prospective cognitive impairment across diet groups among people aged 65 and older, using data from 6 waves of the CLHLS cohort from 2002 to 2018 (Song, 2026).
They defined the diet groups as:
- vegan – abstaining from all animal products
- lacto-ovo vegetarian – consuming dairy and/or eggs but no meat or fish
- pescatarian – consuming fish but no meat
- omnivore – consuming meat at any frequency
Over the course of about 16 years, the vegan group had a trend toward higher rates of cognitive impairment than omnivores (as shown in Figure 3 of their paper). Unfortunately, they didn’t report exact numbers, follow-up duration, or number of measurements. Their Figure 3 indicates that the vegan group had a higher predicted probability of cognitive impairment than omnivores by roughly 1–2% from about age 80 to 100; statistical significance wasn’t reported.
There’s a significant caveat to extrapolating this finding to vegans in general. It seems likely that most of these “vegans” weren’t necessarily choosing to be vegan. Although Song et al. defined vegan as “abstaining from animal products,” there’s nothing to suggest that the diet assessment tool did anything more than measure what people ate, as distinct from what foods they proactively abstain from or what they identify as. That 491 of the 3,554 “vegans” in the study were over 100 years old at baseline adds to my skepticism; it seems very unlikely that the researchers would have encountered so many vegan centenarians, or, if they did, that they wouldn’t have mentioned finding clusters of vegan centenarians. For cohorts that actively recruit large numbers of vegetarians and vegans, such as the Adventist Health Study-2 and EPIC-Oxford, it’s much safer to assume that participants are truly “abstaining” from animal products.
This study also included a cross-sectional arm using baseline characteristics. The vegan group had an odds ratio of being cognitively impaired of 1.32 (95% CI 1.22-1.45, p < 0.001). This was after adjusting for age, gender, social and lifestyle factors (including residence in a city, town, or rural area, and education level), and comorbidities. Adjusting for residence decreased the association for vegans, but didn’t ameliorate it.
Crude prevalence of cognitive impairment among diet groups in the CLHLS, cross-sectional and not age-adjusted, was:
- vegans: 37.9%
- lacto‐ovo-vegetarians: 42.4%
- pescatarians: 33.7%
- omnivores: 34.4%
While the differences in cognitive impairment between the vegan and omnivore groups were statistically significant, they weren’t massive.
Many in the vegan group were from rural areas (67%) and had little or no formal schooling (70%). I couldn’t find evidence of a nationwide program in China that screens rural older people for vitamin B12 deficiency or provides vitamin B12 supplements. If older people avoid or can’t access animal-source foods and also lack B12-rich fortified foods or supplements, that could likely worsen cognition over time.
They also cross-sectionally analyzed two other cohorts: the Survey of Health, Ageing and Retirement in Europe (SHARE) and the United States National Health and Nutrition Examination Survey (NHANES). SHARE didn’t distinguish vegans from other vegetarians. NHANES had 32 vegans who, at baselines, had a non-statistically significant increased odds ratio of cognitive impairment of 1.67 (95% CI: 0.55-5.10) in the fully adjusted model.
While this data is concerning, it’s also not surprising: when animal products are absent from the diet long term, and B12 isn’t obtained from fortification or supplements, B12 deficiency is highly likely and can impair cognition. To understand the impact of a vegan diet on cognition, people who identify as and follow a vegan diet should be purposefully recruited, their vitamin B12 and other nutrient intakes measured, and their cognition assessed over time.
