Current guidelines suggest that all women of childbearing age who are receiving phototherapy should be taking folate supplementation at a dose of 0.8 mg/day to reduce the risk for neural tube defects in any unplanned pregnancies, according to the results of a recent review published in the Journal of the American Academy of Dermatology.
The investigators sought to review the effects of ultraviolet radiation on folate levels and to provide recommendations to women of childbearing age regarding the use of phototherapy. The analysis included in vivo studies that compared folate levels before and after phototherapy sessions, recognizing that photodegradation of folate has been demonstrated in laboratory analyses.
No evidence was presented of decreased folate levels after exposure to ultraviolet A light. Decreased folate levels after sun exposure were limited to individuals who were taking folate supplementation. Studies that used narrowband ultraviolet B light demonstrated mixed results, possibly explained by the dose-dependent degradation of folate.
Exposures of more than 40 J/cm2 cumulatively, and more than 2 J/cm2 per phototherapy treatment session, were both associated with 19% to 27% decreases in serum folate levels; however, lower doses did not affect folate levels.
The limitations of the current review include extensive variability in the study results and a lack of consideration of potential confounders. It is known that the effect of ultraviolet radiation on folate levels in humans is still inconclusive.
The investigators concluded that the heterogeneous results reported from the in vivo studies reviewed underscore the need for larger, controlled studies. Many factors can affect serum folate levels, and an ideal study would control for all these potential confounders. Moreover, as all of the results from the referenced studies were for a mixed cohort of men and women, stratifying the results according to sex would help account for differences in baseline folate levels and response to phototherapy between men and women.
Zhang M, Goyert G, Lim HW. Folate and phototherapy: what should we inform our patients? J Am Acad Dermatol. 2017;77(5):958-964.