29 Jul 2011

Move your body, or else lose your mind? Two papers in this week’s Archives of Internal Medicine online support the idea that exercise can stave off cognitive decline. A five-year observational study led by Kristine Yaffe at the University of California, San Francisco, found that older adults with the highest energy expenditure have the lowest risk for cognitive decline. Analyzing results from the Women’s Antioxidant Cardiovascular Study, researchers led by Jae Kang at Brigham and Women’s Hospital, Boston, Massachusetts, found that regular exercise protected women with vascular disease against the same demise. Reviewing these and prior studies, “I believe that these findings can inform practice and the advice that we give our aging patients,” wrote Eric Larson, from the Group Health Cooperative, Seattle, Washington, in an accompanying editorial. “Clinical research should now be increasingly directed to the development of effective ways to change behavior to promote habitual physical activity, ideally throughout life, but especially in middle and late life.” he adds. The articles appear in the July 25 issue of the journal.

Numerous studies have linked physical activity, or more precisely, lack thereof, with cognitive decline and/or dementia (see, e.g., Weuve et al., 2004; Abbot et al., 2004; Larson et al., 2006). As discussed in the AlzRisk database, the evidence suggests a modest effect. However, most studies have relied on subjective reporting of the intensity and duration of exercise, which often jibes poorly with objective measures of physical activity. Yaffe and colleagues opted for a more precise measure of total exertion: activity energy expenditure (AEE). They determined AEE by the doubly labeled water method, the gold standard for measuring total physical activity. Subjects imbibe a small amount of water comprising stable isotopes of hydrogen and oxygen, and then researchers measure how quickly those isotopes are eliminated to accurately measure metabolic expenditure. The method captures all energy expenditure, even that due to low-intensity activity, for example, moving around the house or fidgeting while working at one’s desk.

Using the isotope method, first author Laura Middleton and colleagues correlated physical activity at baseline with subsequent cognitive decline among 179 healthy older men and women (average ~75 years old) followed for five years. Middleton found that people in the highest tertile of AEE had a 90 percent lower risk of subsequent cognitive impairment compared to those in the lowest tertile of activity. “There was also a really nice dose response,” Middleton told ARF. Though the sample size was relatively small, with only about 15 percent of the cohort showing cognitive decline at follow-up, “The good news is that the study confirms previous findings, but with better measures,” she said. In fact, the correlation was much stronger than that seen in self-reported studies, which is probably due to reliability issues with the latter. “It suggests that even low-intensity activity captured by AEE, but not by self-reports, such as gardening or some household chores like cooking, contribute to protection,” said Middleton. She noted that people are much more likely to report jogging, swimming, or biking than less intensive activities.

Kang and colleagues addressed another shortcoming of previous studies on activity and cognition, namely, their emphasis on healthy volunteers. The researchers wanted to know if physical activity also protected less healthy people who are at higher risk for cognitive decline. First author Marie-Noël Vercambre and colleagues analyzed data from the Women’s Antioxidant Cardiovascular Study, which tested if vitamins E, C, and antioxidants could protect against cardiovascular disease. Some 3,000 older women enrolled in the trial and their cognitive status was assessed by telephone interview at baseline and again every two years for six years. The women were also reported on the previous years’ physical activities, including various sports. “We really wanted to know if activity is beneficial in this population of women who were at higher risk for cognitive impairment,” Kang told ARF. “In the trajectory from healthy to cognitive impairment, where is physical activity important?”

Vercambre and colleagues found that women in the highest quintile of physical activity had a slower rate of cognitive decline. “Cognitively speaking, those most active were five-seven years younger in terms of the cognitive rate of change,” said Kang. He noted that this is quite a remarkable difference, given studies suggesting that delaying onset of dementia by even one year could amount to millions of cases averted by 2040. The researchers were careful to ensure cardiovascular disease itself did not bias the results. Taking out those with the worst health problems, such as myocardial infarctions, did not alter the data; exercise still seemed to help those women with high risk factors. The exercise did not have to be intense, either. Women who took daily 30-minute walks had slower decline in global cognition, verbal memory, and category fluency scores.

Kang noted that this was an observational study, and that definitive answers to whether physical activity can protect against cognitive decline should come from randomized, controlled clinical trials. A small trial carried out in Australia found that a moderate exercise program protected older adults with subjective memory complaints from ensuing dementia (see ARF related news story).—Tom Fagan

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References

News Citations

1. Work Up a Sweat to Stay Sharp, Randomized Trial Suggests 5 Sep 2008

Paper Citations

1. Weuve J, Kang JH, Manson JE, Breteler MM, Ware JH, Grodstein F. Physical activity, including walking, and cognitive function in older women. JAMA. 2004 Sep 22;292(12):1454-61. PubMed.
2. Abbott RD, White LR, Ross GW, Masaki KH, Curb JD, Petrovitch H. Walking and dementia in physically capable elderly men. JAMA. 2004 Sep 22;292(12):1447-53. PubMed.
3. Larson EB, Wang L, Bowen JD, McCormick WC, Teri L, Crane P, Kukull W. Exercise is associated with reduced risk for incident dementia among persons 65 years of age and older. Ann Intern Med. 2006 Jan 17;144(2):73-81. PubMed.

External Citations

1. Women’s Antioxidant Cardiovascular Study
2. AlzRisk database

Further Reading

News

1. Work Up a Sweat to Stay Sharp, Randomized Trial Suggests 5 Sep 2008