Are Vitamin D Supplements an Adequate Substitute for Sun Exposure?

Abstract

It is becoming well understood that low blood levels of 25-hydroxyvitamin D (25(OH)D) are a risk factor for many diseases and other adverse health effects including hypertension, cardiovascular disease, stroke, breast cancer, colorectal cancer, metabolic syndrome, type 2 diabetes, obesity, multiple sclerosis, type 1 diabetes, rheumatoid arthritis, Alzheimer’s disease, autism, schizophrenia, asthma, preterm birth, maternal mortality, myopia and COVID-19. Levels of serum 25(OH)D are at the same time a measure of vitamin D status and, since 70-90% of this biomolecule is produced by sun exposure, a measure of sun exposure. There is some disagreement among scientists as to whether vitamin D supplements are an effective substitute for sun exposure for attenuation of these diseases and adverse health effects. In this paper we review the current state of the science on this subject and conclude that vitamin D supplements are not an adequate substitute for sun exposure for attenuation of most of these diseases and adverse health effects, particularly hypertension and cardiovascular disease, and should not be recommended in lieu of sun exposure to patients presenting with low levels of serum 25(OH)D. Vitamin D supplementation for such patients could even be harmful, because it will raise patients’ serum 25(OH)D levels, thereby giving patients a false sense of security and obscuring the best available metric for insufficient sun exposure.