Sleep, activity, diet and wellbeing: three studies

A study published in PLOS One in 2025 analysed three datasets, totalling 2,086 young adults aged 17 to 25 in New Zealand, the United Kingdom and the United States. It examined how sleep quality, physical activity and fruit and vegetable intake relate to psychological wellbeing: comparing different people, and following the same person from one day to the next.

How the study was done

The first study was a survey, the other two were daily diaries.

In the third, 236 participants wore a wrist device that measured physical activity alongside what they reported. With the device data in place of their answers, the results stayed similar.

The study asks two questions. Do people who sleep better feel better than those who sleep worse? And does the same person feel better on days after better sleep? In all three datasets sleep quality was the factor most linked to wellbeing, at both levels. Fruit and vegetable intake came next.

Physical activity was linked to wellbeing mostly when comparing the same person with themselves, from day to day.

Three habits whose effects add up

The links between the three habits and wellbeing were mostly additive: each adds its own part. With one exception: on days with more fruit and vegetables, the effect of a poor night's sleep on that day's wellbeing appeared smaller. The authors present it as a possibility. The study concerns young adults: it does not say what holds at another age.

The Digital Twin lines up the data your devices write to your phone, such as steps, heart rate and sleep, and shows you how they change over time. It does not calculate risk and it does not diagnose: this research describes groups of people, not you. These are data to read together with your doctor.