Objectives: A paper by Qizilbash et al., published in Lancet Diabetes and Endocrinology in April this year, reported that underweight in midlife increases dementia risk, and contrasting previous research they reported that overweight in midlife lowers dementia risk. This study has been questioned because they considered individuals between 40-80 years of age at BMI assessment as a single group, mixing midlife and late-life BMI. Methods: For this reason, we analyzed separately the dementia risk for three age groups at BMI assessment: 35-49, 50-69 and 70-80 years. Our data includes more than 80 000 participants in Norway followed-up for dementia related mortality, using Cox regression, with a maximum of 38 years of follow-up. Results: Two aspects of our findings need to be considered. First, underweight both in midlife and old age was associated with increased dementia risk. Second, the association between overweight and dementia depended on age at BMI assessment; when BMI was assessed in midlife there was no decreased dementia risk, but when BMI was assessed in old age, high BMI was associated with decreased dementia risk. Conclusions: Obesity involves increased health risk for several conditions. Based on the Qizilbash paper, global news corporations have reported that being overweight in midlife may reduce the risk of dementia. We believe the uncertainties concerning clinical relevance of the Qizibalsh paper findings should be noted, particularly that other studies find no such protective effect of midlife overweight. However, being underweight at different stages in life seems to be associated with increased dementia risk. To gain more knowledge about the associations between weight, dementia and the mechanisms involved, further investigation is warranted.
Qizilbash, N., Gregson, J., & Pocock, S. (2015, July 1). Does midlife obesity really lower dementia risk? - Authors’ reply. The Lancet Diabetes and Endocrinology. Lancet Publishing Group. https://doi.org/10.1016/S2213-8587(15)00220-X