A new study has found that high exposure to UV-radiation is associated with an adverse hormone balance in postmenopausal women.
UV-radiation affects the body through pathways that can have both positive and negative health effects, such as immunoregulation and vitamin D production. Different vitamin D metabolites are associated with higher or lower concentrations of estrogens and have the potential to alter the female sex hormone balance.
"When a woman reaches menopause, we see the levels of estrogens decline and an increase of other hormones, called gonadotropins," explained Kai Triebner, researcher at the University of Bergen.
Triebner along with other researchers from the University of Bergen assessed individual exposure of solar UV-radiation in what they are calling the first large-scale epidemiological study of this kind. The new study was published in Maturitas, the official journal of the European Menopause.
Triebner has studied the hormonal balance of women in relation to menopause for many years. He has examined a number of factors, such as how changing hormone levels impact health and wellbeing, the affects of environmental factors on hormone levels and how to estimate the progress of the menopausal transition.
In fact, Triebner's earlier research has shown that menopause affects women's lung function negatively, and that access to green spaces may postpone menopause. Recently, he has investigated how UV-radiation affects the level of estrogens and gonadotropins.
Triebner now has another study under his belt, most recently looking at sunbathing after menopause.
The study involved data from 580 postmenopausal women across Western Europe. The women were participating in the European Community Respiratory Health Survey (ECRHS). Women who used hormonal medication were excluded from the study.
Using satellite data, researchers were able to develop a model to determine how much UV-radiation the women have been exposed to, depending on where they live.
"The basis for the model is a validation study from ISGlobal in Barcelona where they have used a necklace to measure UV-radiation exposure," said Triebner, who explained that this resulted in a model that gives the researchers a good measure of the individual UV-exposure for every participant included in the study.
The participating women were also asked to state how much time they spend in the sun, which parts of the body are typically exposed and if they use sunscreen.
Researchers also measured the hormone concentrations and compared that to the UV-exposure during the month before.
Other factors were taken into consideration, such as age, skin type, body mass index, and vitamin D intake from dietary sources.
One of the weaknesses that the authors did note is that the dietary assessment of vitamin D did not include supplements and that serum vitamin D levels were not available.
Hormone levels revealed that participants who were most exposed to sunlight had lower levels of estrogen and more gonadotropins compared to those exposed to lower levels of UV-radiation.
"A low estrogen level and a high level of the other hormones increases the risk of osteoporosis, cardiac diseases and neurodegenerative diseases, such as Alzheimer," said Triebner.
The authors reported that the direct association of dietary vitamin D intake with hormones did not yield any statistically significant results, indicating that the role of dietary intake of vitamin D is not a driving force of the observed associations.
“The stratified analyses by season of exposure showed that the associations were considerably stronger for exposure during the sun-rich months, which strengthens the hypothesis that dietary vitamin D intake may be negligible. We found similar results for women with white skin complexion (compared to the main analysis), while for women with non-white skin complexion the associations were less clear. This could however be due to the small numbers of individuals with non-white skin complexion, decreasing the statistical power for the analyses conducted on this subsample,” the authors noted.
The authors explain that one possible mechanism explaining the significant negative association between estrogens and UVR exposure is based on UVR derived vitamin D (cholecalciferol) being metabolized into calcidiol, and 17β-estradiol enhances the conversion of calcidiol to calcitriol, the active form of vitamin D, in the kidneys. They add that this pathway might explain the observed association on estrone, a metabolic intermediate of 17β-estradiol. This mechanism may be further supported by vitamin D being stored in adipose tissue, the major estrogen production site in postmenopausal women.
Residence not a major factor
The participants in the study were a cross segment of Western Europe, hailing from Denmark, Norway, Sweden, Iceland, France, and Spain. According to the researchers, country of residence did not seem to cause a great difference in UV exposure.
"How much vitamin D you need varies from person to person and where you live. As a rule of thumb, ten to fifteen minutes a day in the sun with your face and lower arms exposed is recommended. If you exceed this, you should wear sunscreen, regardless of whether you sunburn easily," said Triebner.
The study highlights a double edged sword, with the researchers suggesting that sun exposure be carefully monitored after menopause, but at the same time, noting that UV light is needed to keep vitamin D levels up for health. This is especially tricky when you factor in how vitamin D metabolites can impact estrogen levels and have the potential to alter hormone balance.
“High exposure to UVR is associated with an adverse hormone balance in postmenopausal women and may negatively affect healthy aging of a large part of the population. This study indicates that managing UVR exposure has potential to influence the hormone balance and counteract adverse health conditions after menopause. Future studies continuing this pioneering work and focusing on pathways, could consider including several vitamin metabolites, not only the routinely measured vitamin D3,” the authors concluded.
“Ultraviolet radiation as a predictor of sex hormone levels in postmenopausal women: A European multi-center study (ECRHS)”
Authors: K. Triebner et al.