Smoking, childhood IQ, and cognitive function in old age.

OBJECTIVES To examine the association between smoking history and cognitive function in old age, and whether it remains after controlling for childhood cognitive ability (IQ) and adult socioeconomic status (SES). METHODS In the Lothian Birth Cohort 1936 Study, 1080 men and women, who previously participated in a nationwide IQ-type test in childhood, were followed up at age 70. The associations between smoking history and age 70 IQ, general cognitive ability (g), processing speed, memory, and verbal ability were assessed. RESULTS Lower childhood IQ was associated with a higher risk of becoming a smoker and continuing to smoke in late life, and with reduced lung function (FEV1) in late life. Current smokers scored significantly lower than ex-smokers and never smokers on tests of age 70 IQ, general cognitive ability, and processing speed, but not memory or verbal ability. After controlling for childhood IQ and SES, current smoking at age 70 (but not pack years of smoking) was associated with impairments in general cognitive ability and processing speed. CONCLUSION Smoking in old age makes a small, independent contribution to cognitive performance in old age.