Does vitamin D help slow prostate growth?
In the lab, vitamin D slows prostate cell growth, but in people that effect has not yet been consistently found. If you have prostate complaints, discuss with your doctor whether vitamin D makes sense for you.
In laboratory and animal studies, vitamin D slows cell growth in prostate tissue. This makes good biological sense: the vitamin acts as a brake on uncontrolled cell division. Whether this also leads to a noticeably slower-growing prostate in people has not yet been reliably shown.
For benign prostate enlargement (where the prostate grows larger and causes urinary problems) the picture is very uncertain. Some studies found a higher risk in people with a particular genetic make-up; others found no link at all. As for taking vitamin D as a supplement: one overview suggested a beneficial effect on urinary symptoms, but that overview combined vitamin D with zinc and other lifestyle changes. That is too little to say anything meaningful about vitamin D on its own.
For prostate cancer (a different condition from ordinary prostate enlargement), two out of eight studies found a drop in PSA levels (a marker of prostate activity) with vitamin D use. One study found a survival benefit. The majority, however, saw no difference. Findings on vitamin D and calcium in relation to prostate cancer risk are also contradictory: a high calcium intake was actually linked to a higher risk in some studies.
If you have concerns about your prostate or are taking medication, discuss with your doctor what vitamin D might mean for you. The available evidence does not support taking vitamin D to prevent prostate cancer.
This answer draws on three analyses examining the link between a gene variant and the risk of benign prostate enlargement, an overview of diet and benign enlargement symptoms, an overview of studies in people with prostate cancer, and laboratory and animal research into cell growth. The researchers themselves point to high inconsistency between studies on gene variant risk and to the absence of quantitative outcomes for vitamin D supplementation in benign prostate enlargement. The evidence for a meaningful effect in people is thin and contradictory.