Higher body mass index is associated with higher death rates from cardiometabolic diseases (i.e., cardiovascular disease, diabetes, and renal disease) (1, 2). However, body mass index reflects both fat and lean body mass, which have opposing effects on risk of cardiometabolic disease (3). Higher levels of fat mass are linearly and positively associated with risk, but higher levels of lean body mass are inversely associated with most cardiometabolic diseases in middle age (3). Higher levels of lean body mass are also inversely associated with falls and fractures in old age. Lean body mass consists of the weight in bone, muscle, ligaments, tendons, and internal organs. A life course approach to understanding the determinants of lean mass is important, including promotion of physical activity and ensuring an adequate intake of protein, calcium, and vitamin D throughout the life course (4). Milk is an important dietary source of both calcium and protein, and drinking a pint of skimmed or semi-skimmed milk provides about 720 mg of calcium (which is almost the full daily dietary requirement of calcium (4). However, there are important ethnic differences in the ability of adults to digest milk because of variable activity of lactase enzyme, which remains higher in northern than …