Footnotes

• Twitter @sadneurons, @lizcoulthard

• Correction notice Since first publication, the sentence 'lower BMI seems protective in later life' has been updated to 'higher BMI seems protective in later life'.

• Contributors Both authors contributed to writing this work.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests EC has received payment from Novartis, Lilly, Eisai, Biogen and UCB for consultancy and/or delivering educational resources.

• Provenance and peer review Not commissioned; internally peer reviewed.