Older people are recommended to take oral vitamin D supplements, but the main source of vitamin D is sunlight. Our aim was to explore whether active encouragement to spend time outdoors could increase the levels of serum 25-hydroxyvitamin D (25(OH)D) and increase the mental well-being of nursing home residents.

A cluster randomized intervention trial.

Nursing homes in southern Sweden.

In total 40 people >65 years.

The intervention group was encouraged to go outside for 20–30 minutes between 11 a.m. and 3 p.m. every day for two months during the summer of 2018.

We analyzed serum 25(OH)D before and after the summer. Data from SF-36 questionnaires measuring vitality and mental health were used for the analyses.

In the intervention group, the baseline median (interquartile range (IQR)) of serum 25(OH)D was 42.5 (23.0) nmol/l and in the control group it was 52.0 (36.0) nmol/l. In the intervention group, the 25(OH)D levels increased significantly during the summer (p=0.011). In the control group, there was no significant change. The intervention group reported better self-perceived mental health after the summer compared to before the summer (p=0.015). In the control group, there was no difference in mental health.

Active encouragement to spend time outdoors during summertime improved the levels of serum 25(OH)D and self-perceived mental health significantly in older people in nursing homes and could complement or replace oral vitamin D supplementation in the summer.