If you’re obese in middle age and you have high blood pressure or other “metabolic abnormalities” — like high blood sugar or low HDL (“good”) cholesterol — you may be setting yourself up for faster cognitive decline over time than your normal weight peers, a recent study found.
The findings add to the mounting evidence that obesity increases the risk of dementia later in life.
The study included 6,401 people who were followed for 10 years. At the beginning of the study, the participants’ average age was 50. About 53% were normal weight, 38% were overweight and 9% were obese. Thirty-one percent of the participants had two or more metabolic abnormalities — including high blood pressure (or taking medication for it), low levels of HDL, high blood sugar (or taking diabetes medication) and high triglycerides (or taking cholesterol-lowering drugs). Among the obese participants, 60% were considered metabolically abnormal.
At three points over the 10-year study, the participants took memory and cognitive tests that gauged their reasoning and verbal fluency skills. A test might ask the participants to write down, in one minute, all the words they could think of starting with the letter S, for example.
Based on the participants’ test performance, the researchers found that those who were obese and metabolically abnormal registered a 22.5% faster cognitive decline than normal weight participants with no metabolic abnormalities. Notably, obese participants who were metabolically normal also saw faster declines in their cognitive skills, compared with metabolically normal adults with a healthy weight.
That finding contradicts the idea that people can be obese and, as long as they’re metabolically normal, also be healthy. “In the last 10 years or so, people started suggesting you could be fit and fat — you could be obese and metabolically healthy and have no health risk,” lead study author Archana Singh-Manoux, research director at Inserm, the French National Institute of Health and Medical Research, told The Wall Street Journal. “All of these [obese] individuals, whether they were metabolically healthy or not healthy, had a poor cognitive profile.”
The researchers also found that people of normal weight who also had metabolic abnormalities showed faster cognitive decline, compared with people of healthy weight who had no metabolic risk factors.
It’s not clear exactly how obesity may be associated with cognitive decline, but the researchers say there are “several plausible mechanisms” underlying the link. Inflammation and heart disease are likely to be involved — previous studies have shown that cardiovascular health and brain health are linked. Further, metabolic abnormalities like high blood sugar and high blood pressure — which are risk factors for diabetes and heart disease — may cause changes in the brain. It’s also possible that other factors typically associated with obesity may harm the brain: lack of exercise and smoking, for instance.
The study is published in the American Academy of Neurology’s journal Neurology.