New studies question if popular supplements harm aging brains

Recent research suggests popular supplements like vitamin D, omega-3 fish oil, and glucosamine may be linked to faster cognitive decline in some older adults, raising new questions about their safety for the aging brain. The findings are preliminary and observational, not proof of causation. Studies published in 2026 found associations between supplement use and cognitive deterioration. Vitamin D users with normal blood levels showed faster decline, omega-3 users over 55 experienced greater deterioration, and glucosamine users had a higher likelihood of progressing from mild cognitive impairment to dementia. Researchers hypothesize aging alters brain metabolism and the blood-brain barrier, changing how supplements affect brain tissue. Experts do not recommend stopping supplements based on these findings, noting users differ in health behaviors and dosages vary. However, they emphasize supplements are biologically active substances lacking age-specific dosing guidance, and the emerging science suggests the question may be "good for whom, and at what age?" rather than simply "good or bad."