This study aimed to investigate the associations between secondhand smoke exposure and dementia, Alzheimer’s disease (AD) and stroke.

This prospective study analyzed Framingham Offspring (FHS-OS) cohort participants with parents in the original Framingham Heart Study (FHS) cohort with known smoking status during offspring childhood. Surveillance for incident events, including dementia and stroke, among offspring participants exposed to parental smoking up to the age of 18 years commenced at examination 9 through 2014 and continued for approximately 30 years.

At baseline, a total of 1683 (56.2%) subjects were not exposed to any secondhand smoke, whereas 670 (22.4%) subjects were exposed to 0–1 packs (20 cigarettes)/day, and 640 (21.4%) were exposed to over 1 pack/day. On follow-up (median: 31 years), 2993 patients developed dementia, including 103 with AD dementia and 315 with stroke. After adjusting for a wide range of established risk factors, participants with the highest exposure to secondhand smoke exhibited increased risks of all dementia, AD dementia and stroke compared with individuals with no exposure [HR 2.86 (2.00–4.09) for dementia; HR 3.13 (1.80–5.42) for AD dementia; HR 1.89 (1.37–2.61) for stroke]. The results remained comparable in the subgroup for individuals with median exposure to secondhand smoke.

Exposure to secondhand smoke may be associated with increased risks of dementia, AD dementia and stroke.