Prostate Cancer Survival Affected by Seasons, Linked to Vitamin D

Allison Gandey

October 08, 2007

October 8, 2007 — Men diagnosed in the summer or autumn months are more likely to survive prostate cancer, a new study suggests. Researchers reporting in the September 1 issue of the Prostate say this may be due to variations in calcidiol, a marker of vitamin D levels.

"The result is striking but consistent with several other studies," one of the authors, Tomasz Beer, MD, Grover C Bagby endowed chair for prostate cancer research and associate professor of medicine at the Oregon Health and Science University, in Portland, told Medscape Oncology. "We need to study the role of vitamin D in cancer development and outcomes."

The results mirror those of a study published last month in the Archives of Internal Medicine (Autier P, Gandini S. Arch Intern Med. 2007;167:1730-1737) . That meta-analysis of randomized controlled trials showed that taking ordinary doses of vitamin D supplements is linked to decreases in total mortality rates.

Vitamin D is a fat-soluble vitamin found in food or supplements that can also be produced in the body after exposure to ultraviolet rays. Sunshine is a significant source of vitamin D because UV rays trigger vitamin D synthesis in the skin. Some research also suggests that vitamin D may help maintain a healthy immune system and help regulate cell growth and differentiation.

In the present analysis, the team of mostly Norwegian researchers, led by Johan Moan, PhD, from the University of Oslo, found that, compared with men diagnosed with prostate cancer in the winter and spring, men diagnosed in the summer and fall had a 20% lower risk of dying within 3 years of diagnosis.

Does Not Prove Vitamin D Determining Factor, Calls for Additional Study

The investigators used data on prostate cancer incidence provided by the Cancer Registry of Norway, which has recorded all cancer diagnoses since 1953. During the observation period, more than 46,200 men were diagnosed with prostate cancer.

The research team analyzed the 3-year survival using the Cox regression method for 2 age groups at different latitudes in Norway.

Patients were divided into 4 groups:

  • Winter (December to February).

  • Spring (March to May).

  • Summer (June to August).

  • Autumn (September to November).

"Summer and autumn months correspond to times when vitamin D is highest," Dr. Beer said in a news release promoting the findings. "Although the study does not prove vitamin D is the determining factor, it does suggest that this possibility should be studied further."

The researchers also looked at whether foods high in vitamin D such as fatty fish, vacations to southern latitudes, age, and latitude of residence in Norway affected survival. They found that none of these factors predicted the risk for death except for the modest effect of age — younger men experienced a slightly better survival rate.

The researchers suggest that photosynthesis of vitamin D decreases with age. They note the capacity of the skin to produce vitamin D is about 40% lower in men 75 years and older than in men 60 years and younger.

"These results suggest the vitamin D status at the time of diagnosis and presumably initial treatment may be important for long-term outcomes in prostate cancer," Dr. Beer told Medscape Oncology. "At this point, the findings are sufficient for hypothesis generation but need to be confirmed."

He points out that the work was an observational study, not a prospective clinical trial. "Vitamin D levels were not measured in individual patients," he added, "and the study can't determine for sure why men who were diagnosed in the summer and fall did better."

The Oregon Health and Science University and Dr. Beer have significant financial interest in Novacea Inc, the maker of calcitriol. Novacea has acommercial interest in the results of this research and technology. The Oregon Health and Science University has reportedly implemented a Conflict of Interest in Research Committee and Integrity Program Oversight Council to manage this relationship.

Prostate. 2007;67:1362-1370. Abstract

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