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Midlife hand grip strength was linked to dementia risk, cognition, and neuroimaging outcomes, data showed.

A 5-kg decrement in hand grip strength in middle age was associated with incident dementia among men (HR 1.20, 95% CI 1.12-1.28) and women (HR 1.12, 95% CI 1.00-1.26) a median of 11.7 years later, reported M. Maria Glymour, ScD, of the University of California San Francisco, and co-authors in .

That decrement in grip strength also was tied to:

• Lower fluid intelligence scores in men (β –0.007, 95% CI –0.010 to –0.003) and in women (β –0.04, 95% CI –0.05 to –0.04)
• Worse odds of correctly responding to a memory task for men (OR 0.91, 95% CI 0.90-0.92) and for women (OR 0.88, 95% CI 0.87-0.90)
• Greater white matter hyperintensity volume in men (β 92.22, 95% CI 31.09-153.35) and in women (β 83.56, 95% CI 13.54-153.58)

Muscle strength in older age has been linked with many health outcomes, including . However, "Almost no evidence is available on whether the association between hand grip strength and neurocognitive outcomes differs between midlife and late life," Glymour and colleagues observed.

"Midlife is a particularly important window; midlife precedes onset of nearly all dementia, and interventions in midlife have the largest benefit to muscle strength," the researchers pointed out.

"Furthermore, evaluating associations in midlife can help rule out reverse causation from dementia to hand grip strength, because symptomatic dementia is very rare before age 65 years," they added. "Examining gender-stratified associations is also important since there may be significant differences in effect sizes due to differences in the distribution of hand grip strength by gender."

The researchers evaluated 190,406 U.K. Biobank participants who had a mean age of 56.5; overall, 54% were women. Participants were 39 to 73 years old and dementia-free when they enrolled from 2006 to 2010. The group was followed for dementia diagnoses until December 2020.

Hand grip strength was measured with a hydraulic hand dynamometer and included one measure from the right hand and one from the left. Fluid intelligence and prospective memory were assessed by touch screen tests at U.K. Biobank assessment visits. A subset of participants also had brain imaging.

Grip strength was associated with cognition both in people under age 65 and those who were older. In models adjusted for age, an Alzheimer's disease polygenic risk score was not associated with grip strength.

Overall, associations were most pronounced for vascular dementia, Glymour and co-authors noted.

"Hand grip strength is associated with cognition in midlife and late life and with white matter hyperintensities volume in midlife for both men and women," the researchers wrote.

"Genetic factors associated with risk for Alzheimer's disease -- variants known to already be exerting subtle cognitive effects in this sample -- had no or negligible association with hand grip strength," they added. "In aggregate, these results suggest that even small changes in muscle strength might have a nontrivial association with vascular dementia risk."

The U.K. Biobank sample had a healthy volunteer bias, and results may not apply to other populations, Glymour and colleagues noted. In addition, the researchers could evaluate only cross-sectional differences in hand grip strength, hindering the ability to assess change for individual participants as it related to cognition.

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