The association of increased body mass index on cardiorespiratory fitness, physical activity, and cognition in adults with down syndrome.

All measurements were taken at one point in time, so the study can show that higher BMI and lower fitness go together but not that one causes the other. Everyone was recruited for a physical activity trial and was sedentary when they joined, so the group had a narrower range of fitness and activity than you would see in the general Down syndrome population, and the activity comparison was small enough that a real difference could have been missed. Only 47 of the 79 people managed the maximal treadmill test and only 65 had usable activity monitor data, so those analyses rest on a subset of the sample. No one in the study had dementia, so the results say nothing about cognition in adults with Down syndrome who have already developed Alzheimer's disease, which was the outcome the authors were ultimately interested in. Everyone had to be able to walk 10 feet unaided, understand directions and speak, so the findings do not apply to adults with Down syndrome who need more support. Weight status was judged by BMI alone, which the authors acknowledge can be less accurate than body fat percentage.

The authors state that no author reports a conflict of interest. The study is registered as a clinical trial (NCT04048759) and the publication is listed as supported by an extramural grant from the National Institutes of Health.

Do not read this as evidence that losing weight would improve fitness or protect thinking in adults with Down syndrome. The measurements were taken at a single point in time as the starting point of an exercise trial, so the study can only show that higher weight and lower fitness occur together. Do not treat the activity figures as a real difference either: the gap between about 12 and about 21 minutes a day did not reach statistical significance.