Sun exposure leads to an increase in bone mass and a decrease in falls. It is generally assumed that since sun exposure also leads to an increase in blood-vitamin D levels, those levels are responsible for those positive effects of the sun. However, in the July issue of Osteoporosis International, there are indications that sun exposure may have some bone-building and bone-protecting effects of its own. The researchers used microtopographical skin changes to quantify cumulative lifetime sun exposure. This method is known as the Beagley-Gibson (BG) method of measuring cumulative sun exposure. After this measurement, they compared lifetime sun exposure to bone-mineral density, risk of falls and risk of fractures in older adults, aged 53-83 years. Vitamin D levels were also assessed in all subjects.
In women, an increasing BG grade (increasing sun exposure) was quite protective; their risk for vertebral fractures was reduced by 66%, and all major fractures were reduced by 25%. For men, bone-mineral density was increased in younger males who showed the most sun exposure. These results were independent of current vitamin D levels. Risk of falls were not changed. We know that being exposed to the sun is very closely associated with better bone strength and have assumed that most of that bone strength is due to higher vitamin D. In this investigation, vitamin D levels had no predictive value. However, there may have been be other factors at play.
What, besides vitamin D, could be responsible for the reduction in fractures? One possibility is this: Outdoor living is necessary for sun exposure, and people who enjoy the outdoors are generally more physically active. It is well-known that exercise builds bone mass and/or strength due to the stress on the bones. That probably happens with any reasonable level of vitamin D.
I opine, that a study conducted in Spain, is perhaps the transcendent research on hip fracture and sun exposure: it showed that women who were sun seekers had only about one-eleventh the risk of hip fracture compared to those who stayed indoors. So, it may be, that to protect our bones, lots of sun exposure, rather than just a little, may be best. Just be sure not to burn. Daily exercise is also imperative. And be sure to eat a healthful, anti-inflammatory diet, which guards against both osteoporosis and skin cancer. Happy sunning.
 Thompson MJW, Aitken DA, Otahal P, Cicolini J, Winzenberg TM, Jones G. The relationship between cumulative lifetime ultraviolet radiation exposure, bone mineral density, falls risk and fractures in older adults. Osteoporos Int. 2017 Jul;28(7):2061-2068.
 Larrosa M, Casado E, Gómez A, Moreno M, Berlanga E, Ramón J, Gratacós J. Vitamin D deficiency and related factors in patients with osteoporotic hip fracture. Med Clin (BARC) 2008;130:6-9.
By Marc Sorenson, EdD. Sunlight Institute
Part of our brain function is influenced by a naturally produced protein called Brain-Derived Neurotropic Factor (BDNF), part of a cascade of proteins that promotes neuron growth and prevents neuron death. Research shows that BDNF has an influence on processes and behaviors such as depression and brain plasticity and has a seasonal variation in concentration that correlates with the amount of ambient sun; BDNF increases in the spring and summer and decreases in fall and winter. The authors of this research summed up their findings thusly: “This finding is important for our understanding of those factors that regulate BDNF expression and may provide novel avenues to understand seasonal dependent changes in behavior and illness such as depression.”
Correct levels of BDNF, however, have many other important and positive effects in the body, including promoting of long-term memory, regulation of mood and perception of pain, reduction of Alzheimer’s disease and Huntington’s disease, and control of epilepsy, depression, anxiety, bipolar disorders, schizophrenia and addiction. In addition, it has positive effects on type-two diabetes, cardiovascular disease and colorectal cancer.
BDNF has been shown to increase significantly after bright light exposure, and in what I would consider to be a remarkably important study, both light exposure and treadmill exercise increased the expression of BDNF in rats, or as the researchers showed, exercise and/or bright light promoted neurogenesis (new nerve cell growth) in the adult rat brain. How important is this finding for adults who are worried about cognitive decline? We are actually seeing an example of new brain cells being built by bright light and exercise. But the researchers were not through with their recommendations. They stated this in their summary: “In view of these findings, we propose that moderate exercise or exposure to sun during childhood can be beneficial for neural development.”
Other research has also indicated that physical activity is positively associated with BDNF.
Add one more natural chemical that is inversely associated with depression and directly associated with sun exposure. We now have vitamin D, serotonin, endorphins, dopamine and BDNF.
Want to maintain your IQ and other brain functions? Would you rather not take the chance of suffering from Alzheimer’s? Embrace the sun, and move your body! Be careful not to burn. And remember that the use of sunscreens may negate many of the sun’s wholesome effects.
 Molendijk ML, Haffmans JP, Bus BA, Spinhoven P, Penninx BW, Prickaerts J, Oude Voshaar RC, Elzinga BM. Serum BDNF concentrations show strong seasonal variation and correlations with the amount of ambient sun. PLoS One. 2012;7(11):e48046.
 Juzeniene A. Beneficial effects of UV‐radiation unrelated to Vitamin D. Presentation at International Symposium Biological Effects of Light June 11 ‐ 12, 2015 Homborg, Germany.
 Tirassa P, Iannitelli A, Sornelli F, Cirulli F, Mazza M, Calza A, Alleva E, Branchi I, Aloe L, Bersani G, Pacitti F. Daily serum and salivary BDNF levels correlate with morning-evening personality type in women and are affected by light therapy. Riv Psichiatr. 2012 Nov-Dec;47(6):527-34.
 Kwon SJ, Park J, Park SY, Song KS, Jung ST, Jung SB, Park IR, Choi WS, Kwon SO. Low-intensity treadmill exercise and/or bright light promote neurogenesis in adult rat brain. Neural Regen Res. 2013 Apr 5;8(10):922-9.
 Gomes da Silva S, Arida RM. Physical activity and brain development. Expert Rev Neurother. 2015 Aug 9:1-11.