Opioid use disorder is defined as a problematic pattern of opioid use that leads to serious impairment or distress. It has emerged as a public health crisis in the United States, affecting as many as two million people aged 12 years and older. A multifaceted approach to reducing opioid use disorders involves targeting preventable environmental factors in addition to restricting opioid prescriptions. One group of researchers investigated the effects of vitamin D status on reward-seeking behaviors like opioid use and sunlight exposure in mice.

Opioid drugs are highly addictive due to their effects on the reward-seeking centers in the brain. Previous research suggests sunbed tanning may be addictive in ways similar to effects of opioids. Exposure to ultraviolet (UV) light causes the skin to produce vitamin D. It also induces the production of beta-endorphins, which are natural opioids with addictive properties. Humans' UV light-seeking behavior may have developed as an evolutionary strategy to maintain adequate vitamin D levels. Whether vitamin D status has an effect on UV light-seeking or prescription opioid-seeking behavior is unclear.

To assess the relationship between vitamin D levels and opioid use disorder, the authors analyzed data from the National Health and Nutrition Examination Survey (NHANES), a long-term study collecting lifestyle and health data from participants in the United States. To determine the effects of vitamin D deficiency on opioid reward sensitivity, opioid-seeking behavior, and pain, the researchers performed multiple experiments with normal mice, mice without functioning vitamin D receptors, and mice without functioning opioid receptors.

Compared to NHANES participants with normal serum vitamin D levels (greater than 20 nanograms per milliliter), those with insufficient vitamin D levels (12 to 20 nanograms per milliliter) were 1.27 times more likely to have opioid use disorder. Participants with vitamin D deficiency (less than 12 nanograms per milliliter) were 1.62 times more likely to have opioid use disorder. In mice, vitamin D deficiency increased the rewarding and pain-relieving effects of UV exposure through altered gene expression in key brain regions. Finally, vitamin D deficiency sensitized mice to the pain-relieving and rewarding effects of opioid drugs, while restoring vitamin D levels to normal decreased both UV-seeking and opioid-seeking behavior.

The authors concluded that the addictive effects of sunlight exposure may be an evolutionary strategy to maintain adequate vitamin D levels and that opioid-seeking may be a consequence of vitamin D deficiency. Their results imply that obtaining and maintaining adequate vitamin D levels through UV light exposure or supplementation may help prevent or treat opioid use disorder.

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• Learn more about vitamin D in our in-progress overview article.