Following on from my research on annual body clocks last week, I came across quite a number of papers associating the season of detection of breast cancer with survival rates.
A 7-year study that was published in 1983, looking at ~3000 female patients showed a peak of breast cancer symptoms in Spring, with a corresponding trough in the Autumn . This has been verified in many other studies across the globe, showing tumour growth and aggression is higher in Spring.
Larger studies went on to determine a link between the survival rate of cancer patients and the seasons the tumour was detected and treatment began. One study of over a million cancer patients in the UK showed that a patient diagnosed in the Summer or Autumn had a greater chance of survival than if diagnosed in the Winter .
A smaller study, under 50 000 women, in Norway also confirmed that a Summer diagnosis increased the chance of survival by 10-15% over a Winter diagnosis . This data was collected between 1964-1992 and looked at the differences in age and the region them women were living. Women under 50 that lived in a region with more sunlight had a better prognosis than those regions with less sunlight. However, although seasonal rhythms were detected, no regional differences were observed, in women over 50.
|Women (under 50 years old) in Norway had a lower risk of dying from breast cancer within 3 years if their detection and treatment began in the Summer, in a region with most sunshine. (Porojnicu et al, 2007)|
So, can sunlight improve survival rates of breast cancer? Or are there other factors, such as a higher number of infectious diseases around wintertime.
There is growing support that vitamin D, a chemical our body makes in response to sunlight, plays a role in survival against cancer . Lab studies have shown that the products our body makes from vitamin D slow down cell growth . Also, seasonality in cancers is more likely to be seen in women than in men, which is consistent with women being frequently reported of having lower vitamin D levels in winter.
One way to look at the link between vitamin D and cancer would be to look at cultures that eat more dietary vitamin D, or have a diet that changes the rate of vitamin D production. Drug companies are also looking into producing the products of vitamin D that may help cancer patients.
The link between vitamin D products and cancer survival still needs to be fully addressed. Until then, the advice is for women to check themselves monthly, and go out and enjoy the summer sunshine. (Don't forget the sunscreen!)
 P. Cohen, Y. Wax, and B. Modan, “Seasonality in the occurrence of breast cancer.,” Cancer research, vol. 43, Feb. 1983, pp. 892-6.
 H.-S. Lim, R. Roychoudhuri, J. Peto, G. Schwartz, P. Baade, and H. Møller, “Cancer survival is dependent on season of diagnosis and sunlight exposure.,” International journal of cancer. Journal international du cancer, vol. 119, Oct. 2006, pp. 1530-6.
 A.C. Porojnicu, Z. Lagunova, T.E. Robsahm, J.P. Berg, A. Dahlback, and J. Moan, “Changes in risk of death from breast cancer with season and latitude: sun exposure and breast cancer survival in Norway.,” Breast cancer research and treatment, vol. 102, May. 2007, pp. 323-8.
 C. Hansen, L. Binderup, and K. Hamberg, “Vitamin D and cancer: effects of 1, 25 (OH) 2D3 and its analogs on growth control and tumorigenesis,” Front Biosci, vol. 25, 2001, pp. 820-848.