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Being Fat Lowers Dementia Risk In Middle And Old Age, Contradicting Everything We Thought We Knew

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In a reversal of much of the prior knowledge of obesity's risks, obesity may offer some protective effects in the brain. Reuters

Mysteriously, carrying a few extra pounds could help you stave off dementia in old age, a new large-scale study finds, as high body mass index (BMI) was found to correlate with lower prevalence of the late-age brain degeneration compared to people who were underweight.

The findings fly in the face of much of the research on obesity’s lifelong health risks. The condition-turned-disease, as of June of 2013, makes people more likely to suffer from heart disease, stroke, high blood pressure, and diabetes. According to the Centers for Disease Control and Prevention, obesity-related conditions are among the top causes of preventable death in the United States.

"We were surprised to find a lower risk of dementia in people who are overweight and obese, as this has not previously been observed," Dr. Nawab Qizilbash, lead author and head of the clinical research organization Oxone Epidemiology, told Medical Daily.

Qizilbash and his team combed through data on nearly two million involved with the United Kingdom Clinical Practice Research Datalink, which includes people 40 years and older. BMI was recorded between 1992 and 2007, and follow-up data were collected until the practice's final data collection date, patient death or transfer out of practice, or the first record of dementia.

Overall, the people with a BMI lower than 20 faced a 34 percent higher risk for dementia than people of a healthy weight, and people with a BMI over 40, classified as morbidly obese, faced a 29 percent lower risk. BMI is sometimes dismissed as an inaccurate measure, since it can’t distinguish between mass due to muscle and mass due to fat, but the optimal range falls roughly between 20 and 25.

The findings held up even after much scrutiny, Qizilbash told The Times of London. “We did a lot of analysis to see if we could explain it, but it just seems to persist.” The team even controlled for obesity’s increased mortality rate, which meant people in the study weren’t developing dementia simply because they lived longer. Other factors, such as frailty, poor nutrition, and genetics, are likely to play a role in the trend. “We couldn’t get rid of it,” Qizilbash said, “so we’re left with this apparent protective effect.”

Future research will need to dig deeper into the link, in order to confirm the trend isn’t anomalous. In 2008, for example, a study of approximately 6,500 people found excess belly fat put people at greater risk for dementia. Even if people weren’t overweight, the trend held. Qizilbash and his team will look ahead to uncovering some of the mechanisms behind the reversal, which could offer key insights.

Speaking to the Irish Times, Professor Stuart Pocock, from the London School of Hygiene and Tropical Medicine, pointed to the other side of the findings, which may not get as much airplay. “We also need to pay attention to the causes and public health consequences of the link between underweight and increased dementia risk which our research has established.”

Worldwide dementia rates are increasing, according to data from Alzheimer’s Disease International. In 2010, roughly 36 million people suffered from the cognitive decline. That figure is set to double every 20 years, to 66 million by 2030 and 115 million by 2050. Population aging is considered the primary driver of the increases.

Source: Qizilbash N, Gregson J, Johnson M, et al. BMI and risk of dementia in two million people over two decades: a retrospective cohort study. The Lancet: Diabetes & Endocrinology. 2015.

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