Vitamin D is an essential nutrient for many animals, including humans, but do dogs need vitamin D in their diet? The answer is a resounding yes. Unlike humans, who can synthesise vitamin D through sunlight exposure, dogs lack this ability. Instead, they must obtain it through their diet.
As more pet owners shift towards raw and home-cooked diets, understanding the role of vitamin D, its sources, and the consequences of deficiencies becomes crucial. In this article, we will explore why dogs cannot synthesize vitamin D from the sun, the risks associated with inadequate dietary intake, and how to ensure proper supplementation through balanced nutrition.

Why Can’t Dogs Synthesise Vitamin D from Sunlight?

Humans and some other mammals produce vitamin D when their skin is exposed to ultraviolet B (UVB) rays from the sun. This process involves the conversion of 7-dehydrocholesterol in the skin to previtamin D3, which is then metabolized into active vitamin D. However, dogs lack sufficient 7-dehydrocholesterol in their skin to facilitate this process (How et al., 1994).

This means that even if a dog spends hours basking in the sun, it will not be able to produce the vitamin D it needs for proper health. Instead, dogs rely solely on dietary sources to meet their vitamin D requirements. There are two main forms of vitamin D: D2 (ergocalciferol), which comes from plant sources, and D3 (cholecalciferol), found in animal-based foods. Vitamin D3 is the preferred form for dogs, as it is more bioavailable and effective in maintaining proper calcium and phosphorus balance.

The Importance of Vitamin D in Canine Health

Vitamin D plays a critical role in various physiological processes in dogs, including:

Calcium and Phosphorus Regulation: Vitamin D helps regulate calcium and phosphorus balance, which is essential for bone health and neuromuscular function (Nap et al., 2018).
Immune System Support: It has immunomodulatory effects, helping to enhance the immune response against infections and inflammation (Liu et al., 2018).
Muscle and Nerve Function: Proper levels of vitamin D help prevent muscle weakness and nerve dysfunction.
Cardiovascular Health: Research suggests that vitamin D deficiency may contribute to heart disease in dogs (Selting et al., 2016).
Cancer Prevention: Some studies indicate that vitamin D may have protective effects against certain cancers in dogs (Selting et al., 2016).

How Much Vitamin D Do Dogs Need?

The National Research Council (NRC) recommends a daily vitamin D3 intake of 50 IU per kilogram of metabolic body weight for adult dogs (NRC, 2006). However, different organisations and researchers suggest varying amounts based on breed, size, and individual health conditions. FEDIAF (European Petfood Industry Federation) nutritional guidelines recommend 552-3200 IU of vitamin D3 per kg of dry matter for adult dogs.

Vitamin D Deficiency in Dogs

Vitamin D deficiency in dogs can lead to a range of health issues, including:

Rickets: A condition characterized by weak or deformed bones in growing puppies due to insufficient calcium and phosphorus metabolism.
Osteomalacia: Softening of bones in adult dogs, leading to pain and fractures.
Muscle Weakness: Dogs deficient in vitamin D may experience muscle tremors, stiffness, and difficulty moving.
Increased Risk of Infections: A weakened immune system can make dogs more susceptible to infections and inflammatory diseases.
Heart Disease: Studies suggest that low vitamin D levels are linked to heart conditions such as congestive heart failure (Selting et al., 2016).

Vitamin D in Raw and Home-Cooked Diets: Are They Lacking?

Raw and home-cooked diets are popular among pet owners who want to provide a natural, wholesome diet for their dogs. However, many of these diets lack adequate levels of vitamin D.

Raw Diets and Vitamin D

Raw diets, particularly those that follow a prey model approach, often include muscle meat, organs, and bones. However, not all parts of an animal provide sufficient vitamin D. The richest natural sources of vitamin D in a raw diet include:

Fatty fish (e.g., salmon, sardines, mackerel or even cod liver oil)
Liver (particularly beef and cod liver)
Egg yolks

If a raw diet does not include these sources IN THE RIGHT QUANTITIES, a dog may not be getting enough vitamin D. Some raw-fed dogs have been diagnosed with vitamin D deficiency due to imbalanced meal plans (Freeman et al., 2013).

Home-Cooked Diets and Vitamin D

Home-cooked diets pose an even greater risk of vitamin D deficiency if they are not properly formulated. Cooking can reduce the vitamin D content in some foods, making it essential to account for this loss. Without careful supplementation, a home-cooked diet may be significantly lacking in vitamin D, leading to health issues over time.

How to Ensure Dogs Get Enough Vitamin D

To ensure adequate vitamin D intake, consider the following approaches:

Feed Vitamin D-Rich Foods: Incorporate natural sources of vitamin D such as fatty fish, liver, egg yolks and cod liver oil if you are feeding a DIY diet
Use High-Quality Commercial Diets: Many commercial pet foods are fortified with vitamin D to meet canine dietary requirements.
Work with a Nutritionist: If preparing a home-cooked diet, ensure it is properly balanced by consulting a professional who can tailor the diet to your dog’s needs.

The Risks of Vitamin D Toxicity

While deficiency is a concern, excessive vitamin D can also be dangerous. Vitamin D toxicity, or hypervitaminosis D, can occur when dogs consume too much vitamin D from supplements or certain toxic sources such as rodenticides. Symptoms include:

Vomiting and diarrhea
Increased thirst and urination
Loss of appetite
Weakness and lethargy
Calcification of soft tissues (kidney, heart, and arteries)

If vitamin D toxicity is suspected, immediate veterinary intervention is required.

Conclusion

Dogs absolutely need vitamin D, but unlike humans, they cannot synthesise it from the sun. They must obtain it through diet, making balanced nutrition crucial. Raw and home-cooked diets often lack sufficient vitamin D unless properly formulated. Deficiency can lead to serious health issues, while excess intake can be toxic.

To keep your dog healthy, ensure their diet includes appropriate sources of vitamin D, or consult with a veterinary nutritionist for guidance on proper supplementation. By understanding and addressing vitamin D needs, you can support your dog's long-term health and well-being.

References

Freeman, L. M., Abood, S. K., Fascetti, A. J., et al. (2013). "Disease prevalence among dogs and cats in the United States and Australia and effects of nutrition." Journal of Veterinary Internal Medicine, 27(1), 11-14.
How, K. L., Hazewinkel, H. A., Mol, J. A., & Voorhout, G. (1994). "Vitamin D metabolism in dogs." Research in Veterinary Science, 56(1), 97-103.
Liu, Y., Song, C. Y., et al. (2018). "Vitamin D and its potential anti-inflammatory and immunomodulatory effects in dogs." Veterinary Journal, 237, 1-7.
Nap, R. C., Bosch, G., Schonewille, J. T., et al. (2018). "Calcium and phosphorus balance in dogs fed raw meat diets." Journal of Animal Physiology and Animal Nutrition, 102(1), 95-104.
NRC (National Research Council). (2006). "Nutrient Requirements of Dogs and Cats." National Academies Press.
Selting, K. A., Sharp, C. R., Ringold, R., & Thamm, D. H. (2016). "Serum vitamin D concentrations in dogs with cancer and associations with tumor type and disease progression." Journal of Veterinary Internal Medicine, 30(3), 1088-1095.

By following these guidelines, you can safely incorporate fish into your dog’s diet while avoiding potential health risks! Want to know if what you are feeding is cutting it for your dog? Complete the FREE DIET ASSESSMENT now.

Do Dogs Need Vitamin D? Understanding Its Role in Canine Health