Exposure to ultraviolet (UV) light is critical for maintaining many aspects of human health. For example, compounds present in the skin react to UV light, initiating the production of vitamin D, a steroid hormone that participates in many physiological processes. Similarly, photoreceptors in the eyes respond to UV exposure, modulating the regulation of circadian rhythms. Findings from a new study suggest that early life exposure to ultraviolet light reduces the risk of developing early-onset multiple sclerosis (MS).

Multiple sclerosis is an autoimmune disorder characterized by the progressive destruction of myelin – the insulating sheath that surrounds nerves and facilitates neural transmission. The disease affects approximately 3 million people worldwide and is twice as likely to manifest in women than men. Symptom onset typically occurs between the ages of 20 and 50 years, but as many as [5 percent of people with MS experience early onset](https://pubmed.ncbi.nlm.nih.gov/11205364/], with symptoms manifesting during childhood or young adulthood.

The study involved 322 children and young adults with MS (ages 3 to 22 years) and 534 healthy participants of similar ages and sexes. All the participants (or their parents) provided information about their medical history, place of residence, and sun exposure.

The authors found that among the participants who reported having spent fewer than 30 minutes outside per day during the previous summer, 19 percent had MS, while only 6 percent did not. When they accounted for other risks associated with MS, such as smoking or being female, they found that those who spent 30 to 60 minutes outside per day were 52 percent less likely to develop MS, compared to those who spent fewer than 30 minutes outside per day.

These findings suggest that early life UV exposure reduces the risk of developing MS. Although these findings were based on observational data and do not assign causality, the authors of the study pointed out that they align with results of other studies suggesting that low UV exposure is associated with other neurological diseases, including Parkinson’s disease, Alzheimer’s disease, and other forms of dementia. Although there is no cure for Parkinson’s disease, evidence suggests that the fasting-mimicking diet may be beneficial in treating the condition. Learn more about the fasting-mimicking diet in this episode featuring Dr. Valter Longo.

• Link to study abstract.