Physical and cognitive function in midlife: reciprocal effects? A 5-year follow-up of the Whitehall II study.

BACKGROUND: Cognitive and physical functions are closely linked in old age, but less is known about this association in midlife. Whether cognitive function predicts physical function and whether physical function predicts cognitive function were assessed in middle-aged men and women.
METHODS: Data were from Whitehall II, an ongoing large-scale, prospective occupational cohort study of employees from 20 London-based white-collar Civil Service departments. The participants, 3446 men and 1274 women aged 45-68 years at baseline (1995-1997), had complete data on cognitive performance and physical function at both baseline and follow-up (2002-2004). A composite cognitive score was compiled from the following tests: verbal memory, inductive reasoning (Alice Heim 4-I), verbal meaning (Mill Hill), phonemic and semantic fluency. Physical function was measured using the physical composite score of the short form (SF-36) scale. Average follow-up was 5.4 years.
RESULTS: Poor baseline cognitive performance predicted poor physical function at follow-up (beta = 0.08, p<0.001), while baseline physical function did not predict cognitive performance (beta = 0.01, p = 0.67). After full adjustment for sociodemographic, behavioural and biological risk factors, baseline cognitive performance (beta = 0.04 p = 0.009) remained predictive of physical function.
CONCLUSION: Despite previous work indicating that the association between physical and cognitive performance may be bidirectional, these findings suggest that, in middle age, the direction of the association is predominantly from poor cognition to poor physical function.