Measurable cognitive decline may begin as early as 45 years of age, according to data from a 10-year study of more than 7,000 adults.
Previous studies have shown limited evidence of cognitive decline before age 60 years, "but the age at which cognitive decline becomes evident at the population level remains the subject of debate," Dr. Archana Singh-Manoux of the Institut National de la Santé et de la Recherche Médicale in Villejuif, France, and her colleagues wrote Jan. 5 in the British Medical Journal.
The scores in most areas (memory, reasoning, and phonemic and semantic fluency) – with the exception of vocabulary – significantly declined in all age groups for both men and women. Controlling for education had no significant impact on the findings.
Of note, reasoning declined by 3.6% in both men and women aged 45-49 years at baseline. By comparison, mental reasoning declined by 9.6% in men aged 65-70 years at baseline, and by 7.4% in women aged 65-70 years at baseline.
The study participants were part of the Whitehall II cohort, a population of British civil servants established in 1985. The study included 5,198 men and 2,192 women who were aged 45-70 years in 1997-1999, when they began cognitive testing (BMJ 2012 Jan. 5 [doi:10.1136/bmj.d7622]).
Cognitive testing consisted of three clinical examinations conducted over 10 years. Each examination included the Alice Heim 4-I (a test of verbal and mathematical reasoning); a test of short-term verbal memory (writing in a 2-minute period as many words as possible from a list of 20 that had been spoken to them); a test of phonemic fluency (writing as many words beginning with "S" as possible in 1 minute); semantic fluency (writing as many animal names as possible in 1 minute); and the Mill Hill vocabulary test.
Although the findings may not be generalizable because of the homogenous, white-collar study population, the results suggest that paying more attention to dementia risk factors such as obesity, hypertension, and high cholesterol in midlife may be more important than previously thought, the researchers noted. Further studies are needed to determine how and whether cognitive trajectories can be modified, and to identify the best age window for successful interventions, they said.
The researchers had no financial conflicts to disclose. The Whitehall II study is supported by a grant from the British Medical Research Council and the British Heart Foundation.