What's in a handshake? Researchers link handgrip strength to cognitive function in mood disorders

Handgrip strength was significantly associated with overall cognition in people with major depression and bipolar disorder, according to a new study published online in JAMA Psychiatry.

“Although handgrip strength has already been shown to be an indicator of risk of developing psychiatric disorders, the potential value of handgrip strength as a marker of cognitive status in psychiatric disorders has not been explored,” wrote investigators led by Joseph Firth, PhD, National Institute of Complementary Medicine Health Research Institute, University of Western Sydney, Campbelltown, Sydney, Australia.

“The aim of this study was to use population-scale data from the UK Biobank to establish how muscular function as measured by handgrip strength relates to cognitive functioning in people with major depression or bipolar disorder and healthy controls,” the authors wrote.

Experts have become increasingly cognizant of the importance of objective physical fitness tests as indicative of cognitive, physical, and mental outcomes in the general population. Handgrip strength is an attractive measure of muscular fitness because it is noninvasive, easily administered, inexpensive, and efficient.

In this cross-sectional, population-based study, researchers gathered data from 110,067 adults in the UK Biobank (a health-oriented study cohort gathered throughout the United Kingdom). The researchers used pre-established criteria to categorize participants into three groups: major recurrent depression (n=22,699), bipolar disorder (n=1,475), and healthy controls (n=85,893).

Researchers excluded subjects with psychosis and those with neurological illnesses that affect cognitive function.

Subjects were given a 15-minute computerized task battery to measure five components of overall cognitive function: visuospatial memory, reaction time, reasoning, prospective memory, and numeric memory. They measured handgrip strength using a hydraulic hand dynamometer.

The researchers used generalized linear mixed models to assess the association between handgrip strength and cognitive function. They controlled for confounding variables including age, educational level, sex, body weight, and geographic region.

They found that in participants with major depression, handgrip strength was a significant predictor of better performance (P < 0.001) on all five cognitive tasks:

• Visual memory (t = −10.8, coefficient −0.146, SE 0.014)
• Reaction time (t = −20.3, coefficient −0.036, SE 0.002)
• Reasoning (t = 10.8, coefficient 0.213, SE 0.02)
• Number memory (t = 6.89, coefficient 0.160, SE 0.023)
• Prospective memory (t = 14.3, coefficient 0.341, SE 0.024)

Notably, the researchers observed comparable results in healthy controls.

In participants with bipolar disorder, handgrip strength was positively associated with improvements in four measures:

• Visual memory (t = −2.48, coefficient −0.129, SE 0.052, P = 0.01)
• Reaction time (t = −6.66, coefficient −0.047; SE 0.007; P < 0.001)
• Reasoning (t = 4.43, coefficient −0.354, SE 0.08, P < 0.001)
• Prospective memory (t = 2.98, coefficient 0.262; SE, 0.088; P = 0.003)

“To our knowledge, this study is the first to identify handgrip strength as a marker of cognitive function in mood disorders,” Dr. Firth and coauthors wrote. “This work could contribute toward handgrip strength providing an easily administered and clinically useful objective tool for routine assessment of cognitive and functional status in people with mood disorders.”

However, the cross-sectional design of this study means that additional longitudinal and mechanistic studies need to be performed to determine causality. Specifically, experts are unsure whether changes in handgrip strength precede cognitive decline or vice versa.

One limitation of this study is that researchers did not incorporate social and occupational data in the analysis. Additionally, the cognitive task battery did not include validated tasks traditionally used to assess social cognition.

“Further investigation is required to assess the effects of resistance training on cognitive functioning in people with depression and bipolar disorder to determine whether muscular function provides not only a biomarker of cognition, but also a potential therapeutic target for reducing the social and economic burden of these conditions,” the researchers concluded.