Low vitamin D levels “prevalent” in early stage prostate cancer?

Vitamin D insufficiency is currently defined as a serum level 25-hydroxy vitamin D that is less than 75 nmol/l. (And there are many who think that a higher minimum level might be appropriate.)

Choo et al. decided to monitor the serum vitamin D levels of a cohort of patients with non-metastatic prostate cancer being treated at their institution in Toronto, Canada. They hypothesized that vitamin D insufficiency might be common in patients with prostate cancer.

They measured their patients’ serum 25-hydroxy vitamin D levels at baseline and annually over a 5-year follow-up period and then analyzed the accumulated data with the following results:

  • Data from 106 patients with a median age of 66.3 years were available for analysis.
  • The mean and median 25-hydroxy vitamin D levels at baseline were 72.4 and 70.0 nmol/l, respectively.
  • 64/106 patients (60.4 percent) met the definition of vitamin D insufficiency at baseline.
  • Season (i.e., time of year) was the only significant variable associated with vitamin D insufficiency.
  • Of a total 477 measurements of 25-hydroxy vitamin D from baseline and yearly follow-ups, 187 (39.2 percent) met the definition of vitamin D insufficiency.

Choo et al. conclude that “vitamin D insufficiency was prevalent among patients with nonmetastatic prostate cancer.”

Now it might be more appropriate to conclude — on the basis of this study — that vitamin D insufficiency was prevalent among men with prostate cancer in Toronto, but actually we can’t be sure that even that is the case based on these data. We don’t know, for example, whether this prevalence of vitamin D insufficiency in this cohort of patients is any higher (or lower) than the prevalence of vitamin D insufficiency in a comparable group of men from the Toronto area with as average age of about 66 who do not have prostate cancer.

Vitamin D insufficiency is not uncommon at higher latitudes. People in northern cities like Toronto spend a great deal of their relatively long winter indoors. Before we all jump to the conclusion that vitamin D insufficiency is strongly associated with a diagnosis of prostate cancer, it seems likely that we need some better data on vitamin D levels in a comparable, “normal” group of men.

8 Responses

  1. My vitamin D lab value is expressed in “ng/ml”. Is there an easy way to convert to “nmol/l”? My particular recent result was 35.4 ng/mL. The normal range is 32.0 to 100 ng/ml.

  2. I live at 8,000 ft. I spend most of my day out of doors.

    I had my vitamin D level checked just prior to my diagnosis of prostate cancer, because the wife was reading all the vitamin D news. My level was as high as it could go without being labeled “toxic”.

    So, this news certainly does not fit with my life.

  3. Bob:

    Yes. I believe there is, but I shall have to look it up and get back to you about that, hopefully later today.

  4. It is probably because you live at high altitude and spend most of your time outdoors that your vitamin D levels are so high. This is part of the point of the commentary on the article referred to above: a low (or a high) vitamin D level is perhaps not necessarily a risk factor for prostate cancer at all — except perhaps in specific, definable categories of men.

  5. It seems to me that this study is worthless without a control of men without prostate cancer from the same latitude area.
    The conversion factor to ng/ml is 0.4006 (i.e., 1 ng/mol = 0.4006 ng/ml).

  6. Thanks for helping me with my homework Ralph … and I agree with your other comment.

  7. In case any readers are not aware of this (as I wasn’t), the conversion factor for ng/ml to nmol/l is different for each substance being measured. The conversion factor stated by Ralph is only good for 25-hydroxy vitamin D and not for anything else.

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