Folate is a form of vitamin B and is an essential nutrient for our health. Folate is naturally found in green leafy vegetables such as broccoli and spinach, asparagus, mushrooms and some organ meats. For supplementation, the synthetic form of folate is known as folic acid.
Folate is possibly best known for its importance for pregnant women and women of childbearing age. Maintaining healthy folate levels is important in preventing a birth defect known as neural tube defects. Neural tube defects occur in the brain, spine or spinal cord of the fetus and can happen in the beginning of pregnancy, sometimes before the woman is aware she is pregnant. A common neural tube defect is spina bifida, a condition where the fetal spinal column doesn’t close all the way, which can lead to paralysis in the legs.
Past research has suggested that sun exposure may degrade concentrations of folate in the body. One theory why we evolved to have dark skin in equatorial Africa is to protect our folate status. The theory is that our skin evolved to strike a perfect balance between getting enough vitamin D and protecting folate status. However, there have only been a few studies looking at the relationship between folate and sun exposure, some finding significant associations and others coming up short on an association.
Of these studies, none have looked at the effects sun exposure might play on folic acid supplementation in women of childbearing age. So, recently, researchers set out to answer this question.
The research team, based out of Australia, recruited 45 women all between the ages of 18 and 47 years old. For two weeks, they supplemented with 500μg of folic acid to reflect the National Health and Medical Research Council recommendations for women of childbearing age. The National Health and Medical Research Council is a public health organization of the Australian government.
After two weeks of supplementation, the women ceased their folic acid intake and underwent one week of self-monitoring their personal sun exposure, physical activity, sunscreen use, and clothing worn in a diary.
After the three weeks of the study, the researchers analyzed changes in folate levels over just the last week. Here is what they found:
- Self-reported sun exposure was significantly associated with a decrease in serum folate levels (p=0.015).
- Those with moderate and high sun exposure experienced a larger decrease in folate levels compared to those with the lowest sun exposure.
- Those with moderate to heavy physical activity had higher folate depletion than those with light daily physical activity (p=0.019).
The researchers concluded:
“In our study investigating the effects of natural solar UV radiation on serum folate status, we observed that significantly greater depletion of serum folate status occurred in participants with higher sun exposures compared to those with lower exposures (p=0.015).”
Additionally, the researchers noted:
“A dose-dependent effect was observed with regard to sun exposure and serum folate depletion, with participants who reported the highest sun exposures experiencing increased depletion compared to those with intermediate exposures and the lowest exposures.”
The researchers added that the observational design of the study means that they cannot know for sure if sun exposure is the direct cause of the decreased folate status in those with the highest sun exposure. Also, the fact that supplementation was completely stopped during measurements of sun exposure means that we cannot know if supplementation would maintain levels throughout sun exposure.
Larger randomized controlled trials need to be conducted to further understand this relationship. Further study will also be important to understand the clinical meaning to this. While they found that reduced folate levels correlated with increased sun exposure, they didn’t look at any clinical outcomes, so it’s not clear if the amount of reduced folate levels is clinically significant.
It is unlikely that sun exposure’s effect on folate levels is harmful, even if it decreases levels. If it were, we’d likely see that higher vitamin D levels (which would correlate with lower folate levels, in theory) correlate with worse pregnancy outcomes. However, we see the exact opposite. Higher vitamin D levels correlate with better pregnancy outcomes.
Regardless, this relationship between sun exposure and folate status is a reminder that sun exposure and health is a complicated subject. Sun exposure carries both risks and benefits. We need to evaluate both. The Vitamin D Council maintains that sensible moderate sun exposure carries more health benefits than risks.