Sunlight May Cut Risk of Advanced Breast Cancer by half

A research team from the Northern California Cancer Center, the University of Southern California, and Wake Forest University School of Medicine has found that increased exposure to sunlight – which increases levels of vitamin D in the body -- may decrease the risk of advanced breast cancer.

In a study reported online this week in the American Journal of Epidemiology, the researchers found that women with high sun exposure had half the risk of developing advanced breast cancer, which is cancer that has spread beyond the breast, compared to women with low sun exposure. These findings were observed only for women with naturally light skin color. The study defined high sun exposure as having dark skin on the forehead, an area that is usually exposed to sunlight.

The scientists used a portable reflectometer to measure skin color on the underarm, an area that is usually not directly exposed to sunlight. Based on these measurements, they classified the women as having light, medium or dark natural skin color. Researchers then compared sun exposure between women with breast cancer and those without breast cancer. Sun exposure was measured as the difference in skin color between the underarm and the forehead.

In women with naturally light skin pigmentation, the group without breast cancer had significantly more sun exposure than the group with breast cancer. The fact that this difference occurred only in one group suggests that the effect was due to differences in vitamin D production – and wasn’t just because the women were sick and unable to go outdoors. In addition, the effect held true regardless of whether the cancer was diagnosed in the summer or in the winter. The difference was seen only in women with advanced disease, suggesting that vitamin D may be important in slowing the growth of breast cancer cells.

“We believe that sunlight helps to reduce women’s risk of breast cancer because the body manufactures the active form of vitamin D from exposure to sunlight,” says Esther John, lead researcher on the study from the Northern California Cancer Center. “It is possible that these effects were observed only among light- skinned women because sun exposure produces less vitamin D among women with naturally darker pigmentation.”

These new findings about breast cancer risk and sun exposure based on skin color measurements are consistent with previous research by John and colleagues that had shown that women who reported frequent sun exposure had a lower risk of developing breast cancer than women with infrequent sun exposure.

The researchers stressed that sunlight is not the only source of vitamin D, which can be obtained from multivitamins, fatty fish and fortified foods such as milk, certain cereals and fruit juices. Women should not try to reduce their risk of breast cancer by sunbathing because of the risks of sun-induced skin cancer, they said.

“If future studies continue to show reductions in breast cancer risk associated with sun exposure, increasing vitamin D intake from diet and supplements may be the safest solution to achieve adequate levels of vitamin D,” says Gary Schwartz, a co-researcher from the Comprehensive Cancer Center at Wake Forest University School of Medicine.

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Light Gives Asteroids Spin

Astronomers have observed an asteroid change the rate at which it spins for the first time, and shown that this is due to a theoretical effect predicted but never before seen. The international team of scientists from Europe and the United States used a range of telescopes to find that the asteroid is rotating faster by 1 millisecond every year.

The acceleration in the rate of rotation is due to heating of the asteroid’s surface by the Sun. Eventually it may spin faster than any known asteroid in the solar system. The Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the way small bodies in the solar system rotate. YORP is a torque due to sunlight shining on the surfaces of asteroids and meteoroids and warming their surfaces, leading to a gentle recoil effect as the heat is emitted. By analogy, if one were to shine light on a propeller over a long enough period, it would start spinning.

Although this is an almost immeasurably weak force, astronomers believe it may be responsible for spinning some asteroids up so fast that they break apart, perhaps leading to the formation of binary asteroids. Others may be slowed down so that they take many days to rotate once. The YORP effect also plays an important role in changing the orbits of asteroids between Mars and Jupiter, including their delivery to planet-crossing orbits.

Despite its importance, the effect has never been seen acting on a solar system body, until now. Using extensive optical and radar imaging from powerful Earth-based observatories, astronomers have directly observed the YORP effect in action on a small near-Earth asteroid, known as (54509) 2000 PH5. This work is reported in two companion papers, in the March edition of Science Express, by Stephen Lowry et al. (Queens University Belfast, UK) and Patrick Taylor et al. (Cornell University, Ithaca, NY, USA).

Shortly after its discovery in 2000, it was realized that this asteroid would be the ideal candidate for such a YORP detection. At just 114m in diameter, it is relatively small and so more susceptible to the effect. Also, it rotates very fast, with one day on the asteroid lasting just over 12 Earth minutes, implying that the YORP effect may have been acting on it for some time. With this in mind, the team of radar and optical astronomers undertook a long term monitoring campaign of the asteroid with the aim of detecting any tiny changes in the spin-rate.

Over a 4 year time span, Stephen Lowry, Alan Fitzsimmons and colleagues took images of the asteroid at a range of telescope sites including the 8.2m Very Large Telescope array and the 3.5m New Technology Telescope of the European Southern Observatory in Chile, the 3.5m telescope at Calar Alto, Spain, along with a suite of other telescopes from the Czech Republic, the Canary Islands, Hawaii, Spain and Chile. With these facilities the astronomers measured the slight brightness variations as the asteroid rotated.

Over the same time period, the radar team led by Patrick Taylor and Jean-Luc Margot of Cornell University employed the unique capabilities of the Arecibo Observatory in Puerto Rico and the Goldstone radar facility in California to observe the asteroid by ‘bouncing’ a radar pulse off the asteroid and analyzing its echo. With this technique astronomers can reconstruct a 3-D model of the asteroid’s shape, with the necessary detail to allow a theoretical YORP value to be derived and compared with the actual observed spin-rate change seen at optical wavelengths. With careful analysis of the optical data, the asteroid’s spin rate was seen to steadily increase with time, at a rate that can be explained by YORP theory. Most significantly, the effect was observed year after year.

Furthermore, this number was elegantly supported via analysis of the combined radar and optical data, as it was required that the asteroid increase its spin-rate at exactly this rate in order for a satisfactory 3-D shape model to be determined.

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