Your Brain in Your 30s

• “When Does Cognitive Functioning Peak? The Asynchronous Rise and Fall of Different Cognitive Abilities Across the Lifespan,” Psychological Science, March 2015. This study was designed to compare the ages of peak performance in various cognitive functions. Researchers analyzed data from standardized memory and IQ tests, as well as from more than 48,000 people who visited the website TestMyBrain.org. They found that different aspects of intelligence peak at different times of life. For example, short-term memory continues to improve until around age 25, peaking at about 35. Read a summary of the study. (A fee is required to access the full study.)

• “Hyperlipidemia in Early Adulthood Increases Long-Term Risk of Coronary Heart Disease,” Circulation, January 2015. Researchers explored the link between moderately high cholesterol (a non-HDL cholesterol level of 160 mg/dL or higher) and future cardiovascular disease (CVD). They included 1,478 people ages 53 to 57 who were part of the Framingham Heart Study, a long-term, multigenerational study of cardiovascular disease risks. At the start of the study, participants did not have heart disease. During follow-up an average of 15 years later, those with the longest exposure to moderately elevated cholesterol levels had a fourfold increased risk of coronary heart disease (CHD) compared with those with normal cholesterol levels. One limitation of the study was the limited age range. Read the full study.

• “Updating the Evidence on the Association Between Serum Cholesterol and Risk of Late-Life Dementia: Review and Meta-Analysis,” Journal of Alzheimer’s Disease, January 2017. This review analyzed the link between high cholesterol and Alzheimer’s disease using data from 17 studies published from 1996 to 2014. The researchers defined high total cholesterol as a measurement higher than 6.5 millimoles per liter (mmol/L). They found that high cholesterol in midlife (ages 40 to 59) may increase the risk of Alzheimer’s disease, but they stressed that more research is needed to confirm this finding. This review was limited by the small number of studies available for certain measures and a lack of information about whether participants took statins to lower their cholesterol. Read the full study.

• “Stress in America 2020: A National Mental Health Crisis,” American Psychological Association, 2020. This annual survey of Americans’ stress levels and how they respond to it was conducted by The Harris Poll on behalf of the American Psychological Association (APA). The survey found that COVID-19 had a significant effect on Americans’ stress levels. Gen Z reported the highest stress, at 6.1 out of 10. By comparison, millennials rated their stress at 5.6, Gen X at 5.2, boomers at 4.0 and older adults at 3.3 out of 10. Read the full report.

• “Stress effects on the hippocampus: A critical review,” Learning & Memory, September 2015. This paper reviews animal and human studies on the effects of uncontrollable stress on the hippocampus, an area of the brain involved in regulating learning and memory. Studies associate long-term exposure to stress with changes to the size of the hippocampus and the links between synapses, the junctions between nerve cells (neurons). Long-term exposures to stress hormones such as cortisol have been shown to cause changes to the hippocampus, reducing the formation of neurons and reducing plasticity — the ability of neurons to change and adapt. Read the full study.

• “Association of Lifetime Cognitive Engagement and Low Beta-Amyloid Deposition,” Archives of Neurology, January 2012. This study included 65 people with normal cognition (average age, 65) who were enrolled in the Berkeley Aging Cohort, a study of brain changes with age. They underwent a series of mental function tests and were given brain scans. Ten people with Alzheimer’s disease and 10 healthy young people were used as comparison groups. They had the scans only but no cognitive tests. Participants were asked to report how often they engaged in mentally challenging activities such as reading books or newspapers, going to the library and playing games. The authors say cognitive activity is one of several lifestyle practices linked to AD that are worth examining in future studies. Read the full study.

• “Education and Dementia in the Context of the Cognitive Reserve Hypothesis: A Systematic Review with Meta-Analyses and Qualitative Analyses,” PLoS One, June 2012. This review looks at the relationship between cognitive reserve — factors such as education that affect the brain’s ability to withstand age-related damage — and dementia. It includes data from 133 studies with a total of more than 437,000 participants. The studies consistently showed that people with lower education were more than twice as likely to develop dementia than those with higher education. In some studies, people with higher education had more brain damage, but it didn’t appear to affect their cognitive abilities. Read the full study. 

• “Dementia prevention, intervention, and care,” The Lancet, December 2017. This report from The Lancet Commission on Dementia Prevention, Intervention, and Care details evidence-based approaches to preventing and treating dementia. It highlights the results of research on preventive measures such as education, including findings that lower rates of dementia are associated with greater education. Evidence suggests that education is one of nine risk factors that contribute to 35 percent of dementia. Less education, particularly not attending high school, is associated with a 59 percent increase in dementia risk. Read a summary of the study. (A fee is required to access the full study.)