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Research suggests seasonal variation in UVB exposure is related to the risk of early mortality in preterm infants

Posted on: August 31, 2015   by  Missy Sturges & John Canell, MD


A recent study published by the American Journal of Perinatology found that high-intensity UVB exposure during fetal development may be associated with a reduced risk of early mortality in preterm infants.

Extreme preterm infants are those who are born before 28 weeks of conception. These infants are born without fully developed lungs, resulting in frequent breathing difficulties. One of the leading causes of preterm infant fatality is attributed to complications associated with the underdevelopment of the lungs.

Respiratory distress syndrome is a dangerous condition which almost always occurs in extreme preterm infants. Vitamin D production during pregnancy is understood to promote fetal lung development, thereby decreasing the severity of respiratory distress syndrome in infants. Recently, Dr. Cannell discussed the role of vitamin D in respiratory distress among newborns.

Several ecologic studies have found that geographical locations exposed to high-intensity ultraviolet B (UVB) radiation are associated with decreased rates of preterm infant mortality. Researchers believe these findings are likely due to the increased synthesis of vitamin D.

Recently, researchers hypothesized that seasonal variation in UVB exposure during weeks 17 and 22 of gestation would be related to the risk of early mortality in preterm infants. The researchers included infants who were born between 23 and 28 weeks gestation and were admitted to the Neonatal Intensive Care Unit of the University of Alabama between July of 1996 and December of 2010. They assessed local UVB exposure by using the standardized UV index scale, which is a tool commonly used to forecast an individual’s risk of UVB overexposure based on their geographical location.  The infants were separated into three groups depending on the strength of solar UVB exposure during weeks 17 and 22 gestation. Group one received low-intensity local UVB exposure, group two received normal-intensity UVB exposure and group three received high-intensity UVB exposure.

Did the researchers observe a relationship between the intensity of UVB exposure and preterm infant mortality? Here is what they found:

  • Overall, the mortality rate of premature infants within 28 days after birth was 18%.
  • Mortality rates were significantly different across the three groups (p = 0.04).
  • High-intensity solar UVB radiation was related to a 30% lower mortality risk when compared with infants in the normal-intensity solar UVB group (p < 0.01).
  • There was no significant change in mortality risk when comparing the low-intensity solar UVB doses with the normal-intensity solar UVB doses.
  • Both low-intensity solar UVB doses and normal-intensity solar UVB doses were associated with a 12% increased risk of mortality.

The researchers stated,

“Our findings suggest that seasonal variation in solar UVB radiation at early stages of fetal lung development is associated with variation in mortality rates of extremely preterm infants.”

They added,

“The difference in mortality rates according to increasing intensity of solar UVB doses was statistically significant and independent of race, body weight (BW), and gestational age (GA); however, linear dose-response relationship was not found.”

Although the researchers successfully confirmed their hypothesis, they also noted some limitations to their findings. Due to the retrospective study design, the researchers were able to show association only, not causality. This also prevented the researchers from accounting for several confounding variables involved in vitamin D production, thereby decreasing the strength of their findings.

The researchers call for prospective studies in order to confirm their preliminary findings on UVB exposure and preterm infant mortality.


Sturges, M. & Cannell, JJ. Research suggests seasonal variation in UVB exposure is related to the risk of early mortality in preterm infants. The Vitamin D Council Blog/Newsletter, August 25, 2015.


Salas, A. et. Al. Seasonal Variation in Solar Ultra Violet Radiation and Early Mortality in Extremely Preterm Infants. American Journal of Perinatology, 2015.

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