Studies have shown that the use of sun-protective measures doesn't adversely affect vitamin D synthesis, but little is known about the effects of sun protection on the clinically relevant potential complications of vitamin D deficiency, such as bone mineral density and the risk of osteoporotic bone fractures. Using data from the cross-sectional National Health and Nutrition Examination Survey (NHANES), researchers examined any potential association of multimodal sun-protective behaviors with bone mineral density and the prevalence of osteoporotic bone fractures among U.S. adults.

Data from 3,418 adults ages 20 to 59 who completed a dermatology questionnaire were included in the study. To characterize sun-protective behaviors, the researchers focused on three practices described in the NHANES data: staying in the shade, wearing long-sleeved clothing, and using sunscreen. The prevalence for frequently (that is, always or most of the time) staying in the shade, wearing long-sleeved clothing, and using sunscreen was 31.6%, 11.8%, and 26.1%, respectively.

In univariate models, individual sun-protective behaviors were associated with decreases in several site-specific and total bone mineral density z scores. These associations faded in multivariate-adjusted models, except for a possible decrease in lumbar spine bone mineral density with moderate sunscreen use, especially in older adults. The researchers found no increased risk of osteoporotic bone fractures in those who practiced sun-protective behaviors. In fact, moderate-to-frequent staying in the shade was associated with a lower risk of osteoporotic spine fracture, possibly because of sustained patterns of self-protective behaviors.

Because of the cross-sectional design of the data set used in this study, the researchers couldn't determine the causality of associations or provide long-term data on included individuals. Also, they note, the data don't distinguish between the use of sunscreen and other types of sunblock (such as moisturizer with SPF) or the specific type (spray or lotion), strength, or amount of sunscreen used. Additionally, some of the fractures reported could have been due to trauma, they say.

Afarideh M, et al JAMA Dermatol 2021;157(12):1437-46.