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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Researchers suggest vitamin D sufficiency range and its relation to risk of cancer in dogs

A new study published in Veterinary and Comparative Oncology examined the vitamin D status of dogs to determine a range of sufficiency. The study also showed that low vitamin D levels were associated with an increased risk of cancer.

Since research has shown that the effects of vitamin D extend beyond bone health, vitamin D sufficiency has been extensively evaluated in humans. However, little research has been conducted in dogs.

Researchers recently created the first study to examine the range of vitamin D sufficiency in dogs. The researchers were also interested in how low vitamin D levels related to the risk of cancer.

In the study, the researchers defined sufficiency as the point at which vitamin D status was met by a near maximum suppression of the parathyroid hormone (PTH).

Normally, when vitamin D levels are low the body produces PTH to pull calcium from the bones to meet the body’s needs, since a lack of vitamin D reduces the body’s ability to absorb calcium from the diet.

When vitamin D levels are sufficient for bone health, the production of the PTH is maximally suppressed indicating that vitamin D is effectively absorbing calcium from the diet to meet the body’s needs.

The researchers analyzed at what vitamin D range the PTH was maximally suppressed in 282 dogs and found it to be in the range of 100-120 ng/ml.

The researchers then analyzed the relationship between the dogs’ vitamin D levels and the prevalence of cancer and found that dogs with a vitamin D level below 40 ng/ml were 3.9 times more likely to have cancer.

This correlates with research in humans indicating an increased risk for many cancers in individuals with vitamin D levels below 40 ng/ml.

“Serum vitamin D measurement can identify dogs for which supplementation may improve health and response to cancer therapy,” the researchers concluded.


Selting K., et al. Serum 25-hydroxyvitaminD concentrations in dogs – correlation with health and cancer risk. Veterinary and Comparative Oncology, 2014.

14 Responses to Researchers suggest vitamin D sufficiency range and its relation to risk of cancer in dogs

  1. Rita and Misty says:

    My Australian Shepherd, Misty, (pictured here next to me) is approximately 15 years old.

    She is healthy for an old girl, but recently she suffered from the inability to use her hind legs. Also, she had taken to stumbling and falling when she was finally able to get up.

    I’ve given Misty vitamin D for going on 3 years now. But cautious doses–7,000 to 14,000 iu D3 weekly. Misty is the size of a five year old–around 60 pounds.

    Four weeks ago, I thought the time had come for me to make that hard decision. Misty had become completely immobilized. To give you an idea about how I feel towards Misty: I would immediately give 10 years off my life so that she might have 10 more….

    So, faced with a bleak alternative, I bolus-dosed Misty on D3. I gave her very large amounts of D3 for three (3) days. Then I dropped down to 4,000 iu D3 daily, and she continues on this dose now.

    What were the results? Nothing short of miraculous. Misty is walking again. Slowly, yes. No running…and she is a bit stiff…but she stumbles rarely now…and she does not fall.

    I know Misty is old, and that her days are numbered. But my hope for her is that she may rest that final rest gently in her sleep.

    And on that day, VDC, I will call you to take our photo down. Because I will not be able to face her face in cyberspace for a very long time. And I hope on that day you will humor my sadness quickly. Thank you.


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  2. I know that at levels of 32 ng most people lower their PTH, and at 40 ng. still a higher percentage lower it. But has anyone done studies to see the level of 25-hydroxyvitamin D that the PTH is maximally lowered in humans and wouldn’t that consist of evidence as to what the true ideal level is in humans?
    Robert Baker MD
    Internal Medicine

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  3. Rita and Misty says:

    Robert–from the below-linked journal article:

    “The threshold of 25OHD needed to maximally suppress intact PTH has been suggested as a marker of optimal vitamin D status….The point for near maximal suppression of PTH by 25OHD for all women (body mass index, 31.4 ± 7.7 kg/m²) occurred at a 25OHD concentration of 21.7 ng/mL (95% confidence interval, 28-48 ng/mL).”

    If I understand the above quote correctly, the authors are saying that approximately 22 ng/ml is optimal. Of course, I disagree with 22 ng/ml being an optimal vitamin D blood level.

    The link goes to full text. I would enjoy your thoughts, as perhaps I am misinterpreting the journal article.


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  4. Rita and Misty says:

    Robert~also the article speaks specifically on the effect of obesity on the relationship between serum parathyroid hormone and 25-hydroxyvitamin D in women.

    But the information quoted in the article with respect to 22 ng/ml being the 25(OH)D level for near maximal suppression of PTH is confusing to me, especially as you state levels of 32 ng/ml to 40 ng/ml.

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  5. A 17 year-old dog was rejuvenated with 4,000 IU daily vitamin D

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  6. Rita and Misty says:

    Misty has certainly regained some quality of life. I only wish I had thought of before and after pictures.

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  7. Ian says:

    Rita: This:
    “The threshold of 25OHD needed to maximally suppress intact PTH has been suggested as a marker of optimal vitamin D status….The point for near maximal suppression of PTH by 25OHD for all women (body mass index, 31.4 ± 7.7 kg/m²) occurred at a 25OHD concentration of 21.7 ng/mL (95% confidence interval, 28-48 ng/mL).”

    Is for obese women. The value for non-obese could be very different. Also the level of serum calcium for these women was stabilized (They don’t say how). If the blood calcium level is stabilized by supplementation then the PTH may already be low, would it not?

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  8. Rita and Misty says:

    Hi Ian..

    Thank you for your response!

    Yes, I did know that the article speaks to obese women (body mass index, 31.4 ± 7.7 kg/m²).

    I would have thought that near maximal suppression of PTH by 25(OH)D for obese would be at a higher level than 22 ng/ml. My line of reasoning (though not very scientific) is that extra body weight would require higher levels of D for the body to work efficiently.

    However: now that I think a bit, isn’t it often stated that being small and thin-boned is a risk for osteoporosis?

    Perhaps then, generally speaking, obese are less at risk for bone conditions like osteoporosis? Perhaps there are some protective hormonal factors, like additional estrogen, that are to be considered? Perhaps this may factor into the results of the study that I linked above, with a lower 25(OH)D (22 ng/ml) threshold maximally suppressing PTH for obese–as the body’s needs for calcium are being met by other means? Thinner women produce less protective estrogen, so it would make sense that maximal suppression of PTH would be at a higher 25(OH) level, right?

    Please let me know your thoughts.

    And yes, if one supplements with calcium, it makes sense that the PTH may already be low.

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  9. For a long time laboratories listed 20 ng as the normal 25OH vitamin D level.. Only less than 10 years ago did lab seem to accept 32 to 100 ng. I have heard from multiple sources that the figure of 32 ng was obtained by studies that showed that the PTH significantly decreased in most people when the level was 32 ng. But I also heard that additional people further surpressed the level of PTH up to the 25OH vit D level of 40, therefore on that basis a very strong case could be made that the minimal level in humans should be 40 (although other unrelated research shows benefits at higher values). I haven’t studied the research papers myself. The abstract above is we are interpreting it correctly cannot be correct. Much osteoporosis is found at levels of 20 ng of 25OH vitamin D.
    Also I would like to point out in the study above in dogs the maximal surpression is at levels of 100 ng. to 120 ng. Why would humans be so different? And I would also like to point out that the human body will not synthesis vitamin D to achieve a level over 150 ng according to the classic New England Journal of Medicine study (although I’m not saying that someone should take supplements to achieve a level that high).
    Robert Baker MD

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  10. Matt Rhodes says:

    Rita, look at the figure supplied with the abstract. It shows the data for obese, non-obese & the total population. Notice that for the obese group the PTH numbers are much higher to start with, so increasing vitamin D levels has a more pronounced effect. Yes, there is a break point in the fitted curve around 14 & another around 20 ng/ml, but the curve is far from levelled out & it fits the obese data very poorly. Notice both the obese & non-obese groups have a 2nd breakpoint in their curves around 50 ng/ml. I think they are pushing the data way too far to say 20 ng/ml maximally suppresses PTH, since it continues to drop above those levels. 50 might be a better choice, but really more data is needed to assess what happen above 50. This is just one way of estimating optimal vitamin D too. A graph of total cancer rates vs. D level might have different breakpoints.

    Pats to Misty. You might try kicking her up to a higher level (8k/day) temporarily to check whether it gives her anymore benefits. I doubt it would hurt her or you more than her being put to sleep & musculoskeletal pain is a common symptom with D deficiency. A bolus dose is a step in the right direction, but it’s not an immediate cure. The body needs time to soak the D up. You can also get glucosamine/chondroitin supplements for dogs which can also help with joint pain. Gave my sister’s labrador another year or so. She loved the treats & showed a lot more puppy after she went on them.

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  11. Rita and Misty says:

    TY Matt

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  12. How does a dog (or a cat) get vitamin D in the first place? I assume through diet only, so one should look for pet food that contains a appreciable amount. Otherwise, in the wild, dogs and felines get it from consuming the livers, etc., of their prey. What about the needs of ruminants, mice, rabbits? I had never assume that there was a need here. This is a whole new idea for me.

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  13. Tom Weishaar says:

    Defining vitamin D status by secondary hyperparathyroidism in the U.S. population is probably a better study for looking at the relationship between 25(OH)D and PTH in humans.

    From the conclusion of the abstract, “Optimal vitamin D status, defined by estimated maximum PTH suppression, does not occur until at least 25(OH)D levels ≥40 ng/mL.” There aren’t enough individuals in the NHANES database with 25(OH)D levels over 40 ng/mL to say anything with statistical confidence about higher levels.

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