Study Offers Clues on How Bariatric Surgery Improves Cognition

Boston—For years, clinicians have known that neurocognitive function improves after bariatric surgery, but little has been known about what exactly drives this. Now, a new study presented at Obesity Week (abstract 1001) provides some clues.

“Weight loss and improvements in inflammation and metabolic syndrome are correlated with improvements in memory and attention,” said lead author of the study John Morton, MD, director of bariatric surgery at Stanford University School of Medicine, in Standford, Calif., and president of the American Society for Metabolic and Bariatric Surgery.

Growing evidence has linked obesity with poor neurocognitive function and the risk for developing dementia and Alzheimer’s disease (J Alzheimers Dis 2012;30:S89-S95). Studies also have shown that indviduals who undergo bariatric surgery realize improvements in memory and other cognitive domains (Am J Surg 2014;207:870-876).
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But what spurs these gains? By undergoing bariatric surgery, individuals not only lose a significant amount of weight, but they also have significant improvements in glycemic control, metabolic syndrome (MetS), depression and daytime sleepiness, all of which could independently improve cognition.

To pinpoint the specific mechanisms involved, Dr. Morton and his colleagues enrolled 47 consecutive bariatric surgery patients. The average preoperative body mass index was 46 kg/m2; the average age was 48.1 years; 32.6% of patients were diabetic; and 43.9% of patients had MetS.

Study participants completed a battery of cognitive tests before surgery and then at three, six and 12 months after bariatric surgery. The cognitive tests included the revised Hopkins Verbal Learning Test (HVLT), a brief verbal line learning and memory test with six alternate forms; the Digit Symbol Substitution Test; and Trail Making Tests A and B. Patients also completed the Beck Depression Inventory-II; the Epworth Sleepiness Scale; and the Psychomotor Vigilance Task-192, a validated measure of reaction time and psychomotor function.

Preoperative test scores showed that patients were well below population averages in HVLT immediate recall (T score 38.3) and HVLT delayed recall (T score 41.4), and had slower mean response speeds on the Psychomotor Vigilance Task-192 (norms 2.48 seconds vs. patients 3.63 seconds; P<0.05).

Diabetes was the single biggest factor found to affect cognitive scores, according to the researchers. Patients without preoperative diabetes had significantly faster times on Trail Making Test B (diabetes 90.4 seconds vs. no diabetes 63.1 seconds; P=0.039).

“The brain is a big consumer of glucose for its size,” said Dr. Morton. “It consumes a lot more glucose than your heart or your muscles. It really needs it, and when there are derangements in the glucose metabolism, some of the brain chemistry doesn’t work as well. The actual synaptic firings across neurons are impeded.”

At 12 months postsurgery, patients had improved memory and attention, as measured by the HVLT immediate recall (+2.63; P=0.004), the HVLT delayed recall (+1.04; P=0.003) and the Trail Making Test A (–7.25 seconds; P<0.001). Changes in sleepiness and depression did not correlate to changes in cognitive function. Patients without preoperative MetS had significantly greater three-month improvements in HVLT immediate recall (MetS +0.50 vs. no MetS +4.14; P=0.024). Improvements in HVLT immediate recall were strongly correlated with improvements in inflammatory markers at three months, triglyceride/high-density lipoprotein (HDL) ratio (r=0.603; P=0.006) and C-reactive protein (r=0.538; P=0.021), as well as the percentage excess weight lost (r=0.452; P=0.035) at three months.

“All of the patients lost weight at the usual rate that we expect, roughly about 70% of their excess weight in one year,” said Dr. Morton. “Triglycerides and HDL are markers for metabolic syndrome. Think of a lot of these [neural] pathways as being like highways. When you have all that inflammation, you have a clogged highway, and the normal processes are just slower,” said Dr. Morton. “The neurons are preoccupied with inflammatory markers and aren’t doing their usual job.”

The bottom line, said Dr. Morton, is that before bariatric surgery, patients scored well below the national norms on cognitive tests, and after surgery, they normalized or scored similarly to their nonobese peers. These improvements were tied to inflammation and MetS.

John Gunstad, PhD, associate professor in the Department of Psychological Sciences, Kent State University, Kent, Ohio, has been studying neurocognitive function as it relates to cardiovascular disease and obesity for the past 10 years.

“Although obesity is bad for your brain, losing weight can help improve your memory and other mental abilities,” Dr. Gunstad told General Surgery News. “This study provides another clue toward understanding how the weight loss following bariatric surgery helps to improve brain function.”