The study found that the men who had aggressive prostate cancer had lower levels of vitamin D - significantly lower than what is considered normal.
The study - led by Northwestern University of Evanston, IL - is published in the Journal of Clinical Oncology.
The finding offers useful information for cases where patients have agreed with their doctor that the treatment should be "watchful waiting" for the time being rather than removal of the prostate or some other medical procedure.
Lead investigator Adam Murphy, an assistant professor of urology, says:
"Men with dark skin, low vitamin D intake or low sun exposure should be tested for vitamin D deficiency when they are diagnosed with an elevated PSA or prostate cancer. Then a deficiency should be corrected with supplements."
The new study correlates vitamin D in blood sampled a couple of months before surgery to remove the prostate - radical prostatectomy - with an assessment of disease aggressiveness at time of surgery.
The link may explain some disparities seen in prostate cancer in different groups of men - for example in black men, says the team.
In previous investigations, Prof. Murphy and colleagues have found that black men who do not have much exposure to sunlight are up to 1.5 times more likely to be deficient in vitamin D than white men.
Indoor jobs and long winter make it hard to maintain vitamin D levels
For their new study, the team used data from a larger ongoing study of vitamin D and prostate cancer in 1,760 men in the Chicago area.
- Men aged 50 years and older are at higher risk for prostate cancer
- Having a father, brother or son with prostate cancer also brings a higher risk
- Many men with prostate cancer - especially if it has not spread - die of other causes without ever experiencing symptoms from the cancer.
They focused on 190 men of average age 64 who had a radical prostatectomy - surgery to remove their prostate - from 2009-2014. When they underwent surgery, it was found that 87 of the men had aggressive prostate cancer.
Aggressive prostate cancer means tumor cells have started to migrate outside of the prostate. It is also defined by a high Gleason score that indicates the tumor tissue is very different from normal tissue and thus more likely to spread. Prostate tumors with a low Gleason score have tissue that looks very similar to normal tissue.
The men identified as having aggressive prostate cancer had a median vitamin D level of 22.7 ng/mL, which is significantly lower than the 30 ng/mL considered as normal.
The men who did not have aggressive prostate cancer had a median vitamin D level of 27 ng/mL.
Prof. Murphy notes that in Chicago, the average vitamin D level during the winter is about 25 ng/mL. He suggests that because vitamin D is important for bone health and can be a biomarker of other diseases too, then:
"All men should be replenishing their vitamin D to normal levels. It's smart preventive health care."
Prof. Murphy believes most people in Chicago - particularly in winter - should take vitamin D supplements, and concludes:
"It's very hard to have normal levels when you work in an office every day and because of our long winter."
In the US, prostate cancer is the most common non-skin cancer in men. According to the Centers for Disease Control and Prevention (CDC), in most cases, prostate cancer grows slowly and does not cause a health problem.
The prostate specific antigen (PSA) test may show that there is a problem in the prostate, but it can also be high for other reasons.
In December 2015, Medical News Today learned that a long-term trial of a gene therapy that causes the immune system to attack tumor cells found it is effective and safe for the treatment of prostate cancer.