Chinese seniors with mild cognitive impairment had half the vitamin D of their peers (15 vs 29 ng)
Association between serum 25-hydroxyvitamin D levels and cognitive function among older adults in Tianjin, China: a cross-sectional community-based study
BMJ Open, 2026, https://doi.org/10.1136/bmjopen-2025-115914
Ziyan Lou, Xinze Han, Xiaomin Wu, Keran Duan, Xian Cai, Liping Zu, Lingyan Liu, Fei Ma
Summary by Claude - August, 2026
Older adults with mild cognitive impairment (MCI) had roughly half the vitamin D level of those without it — 15.6 ng/mL versus 29.4 ng/mL. That is the headline from this cross-sectional study of 866 community-dwelling adults aged 65+ in four Tianjin neighborhoods, 12.0% of whom met revised Petersen criteria for MCI. Average age was 76.7; two-thirds were women. Blood was drawn fasting and measured by LC-MS/MS, the reference method. Anyone already taking vitamin D supplements was excluded, so these are unsupplemented levels: group average 27.8 ng/mL, range 7.4 to 43.1.
After adjusting for age, gender, education, cholesterol, blood pressure, hypertension, heart disease, diabetes and stroke, higher 25-OH-D remained associated with lower odds of MCI. Cognition was scored with the WAIS-RC. Vitamin D tracked with full-scale IQ and verbal IQ — specifically the information, similarity and vocabulary subtests — but showed no association with performance IQ or any of its five subtests. The associations did not differ by age, gender or education.
What this does not show: nothing about cause. This is a snapshot, not a trial, and the effect sizes on IQ were small (about 0.12 IQ points per ng/mL). The authors themselves note that the risk of reverse causality cannot be overlooked — cognitive decline reduces going outdoors, which lowers vitamin D. Blood was collected March through June and season was not adjusted for, nor were sun exposure, physical activity or BMI. No one was supplemented, so the study cannot say whether raising a level helps. Single city; data collected in 2016.
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