US adults who remember drinking milk daily at age 5 to 12 blew out about 230 mL more air in a second than those who never did. Only 81 people were in the 'never' group, and the memories were decades old

Lungs keep growing through childhood and the teens, and may not reach their best until early adulthood, so researchers keep asking whether what children eat leaves a mark decades later. A team from several Chinese universities and hospitals looked at one everyday food, milk, and published the result in Food Science & Nutrition on 26 October.

They used NHANES, the long-running US health survey, for the years 2007 to 2012. Trained technicians gave adults aged 20 and over a spirometry test in a mobile clinic, which measures how much air a person can blow out in the first second (FEV1) and in total (FVC). The same adults were asked how often they drank milk at three stages of life: ages 5 to 12, 13 to 17, and 18 to 35. People with asthma were left out, leaving 3,935, with an average age of 47.

Compared with adults who said they never drank milk at 5 to 12, those who said once a day or more had an FEV1 about 230 mL higher (95% CI 46 to 414) and an FVC about 324 mL higher (120 to 529), after allowing for age, sex, race and ethnicity, education, marital status, income, height, weight, BMI, smoking, smoke at home, recreational activity and asthma in the family. On our arithmetic that is about 7% of the group's average for each measure. People who drank milk one to six times a week came out almost the same as the daily drinkers (221 and 281 mL), and those who drank it less than weekly showed no gap in FEV1 (minus 3.7 mL). The ratio of the two measures, FEV1/FVC, which is used to spot narrowed airways, did not differ. Milk in the teens and at 18 to 35 showed no significant link with either measure.

Now the caveats. Almost everyone drank milk as a child: weighted to the US population, 88% said daily and only 1.6% said never. That 'never' group was 81 people, and every comparison is against them, which helps explain why the confidence intervals are so wide. A child who never drank milk may have had an allergy, an intolerance, a different family diet or less money at home, and the survey can't separate those. The authors themselves name childhood circumstances, overall diet and growth as things the data did not fully capture. They also point out that the milk memories were collected only once, in adulthood, that they cover how often but not how much or what type, and that today's habits can colour them. Allowing for the other factors already shrank the FEV1 gap by about a third, from 348 to 230 mL.

The gap looked larger in non-smokers (FEV1 307 mL, FVC 495 mL) and in people with no smoker at home (384 and 537 mL), and these splits passed a formal interaction test. The authors still call all the subgroup findings exploratory because so many comparisons were run. Their own conclusion is unusually plain: the results should not be read as evidence that milk directly builds lungs, or that drinking more in childhood would improve adult lung function or prevent lung disease. It is a signal worth testing in studies that follow children forward and record their diet at the time. For a parent, it adds little to the existing reasons to give or not give a child milk.