In dog nutrition, it is not enough for vitamins and minerals to be present in adequate amounts—what also matters is their mutual ratios and interactions. These relationships influence how well nutrients are absorbed, how they are stored, and how they function in the body. Some nutrients enhance each other's effects (synergy), while others can interfere with each other's function (antagonism).
This balance is especially important for growing dogs, pregnant bitches, sporting dogs, and animals that are ill or recovering. In these life stages and situations, the margin for error is smaller, and nutrient imbalances may show up more quickly. That is why it is useful to understand not only individual nutrients, but also how they work together.
The most important vitamin–mineral interactions
1. Vitamin E and selenium (Se)
Synergistic effect – cell protection and immune defence
- Both are antioxidants that protect cells from oxidative damage.
- Selenium is part of an enzyme (glutathione peroxidase) that functions together with vitamin E.
- This is an essential combination, especially for muscle health and overall immune resilience.
Selenium must not be given in excessive amounts—small overages can be toxic.
2. Vitamin D and calcium (Ca) + phosphorus (P)
Essential interaction – skeleton and metabolism
- Vitamin D regulates the absorption and balance of calcium and phosphorus.
- Without sufficient vitamin D, calcium does not absorb properly, even if the diet contains plenty of calcium.
- The calcium–phosphorus–vitamin D balance is particularly important for puppies and large breeds.
The Ca:P ratio should be 1.2–1.4:1 for growing dogs.
3. Vitamin A and zinc (Zn) + iron (Fe)
Partly synergistic effect – skin, mucous membranes, and blood formation
- Vitamin A supports the wellbeing of the skin, mucous membranes, and eyes, together with zinc.
- Iron affects how vitamin A is stored in the liver and how it is transported in the body.
- A vitamin A deficiency can weaken zinc's function in the skin and in immune defence.
4. Vitamin C and iron (Fe)
Synergistic effect – iron absorption
- Vitamin C converts iron into a form that is more readily absorbed (Fe²⁺) in the intestines.
- Although dogs can produce vitamin C themselves, stress, illness, and high activity levels can increase the need.
- Vitamin C also supports collagen formation (connective tissues, joints, skin).
5. Excess fat-soluble vitamins (A, D, E, K)
Potential disruptions
- For example, excessive vitamin A can interfere with the utilisation of vitamin D and vitamin E, and it may cause skeletal problems or liver damage.
- For this reason, fat-soluble vitamins require particular caution in supplements, especially with home-cooked feeding and BARF diets.
Summary
| Vitamin | Affects mineral | Type of effect | Effect |
|---|---|---|---|
| Vitamin E | Selenium | Synergistic | Antioxidant effect |
| Vitamin D | Calcium, phosphorus | Synergistic | Skeletal development, mineral balance |
| Vitamin A | Zinc, iron | Synergistic | Skin, immune system, circulation |
| Vitamin C | Iron | Synergistic | Iron absorption, connective tissue |
| Excess A/D | Several minerals | Antagonism | Toxicity, absorption disturbances |
Sources:
- NRC (2006). Nutrient Requirements of Dogs and Cats.
- Case et al. (2011). Canine and Feline Nutrition, 3rd ed.
- Hand et al. (2010). Small Animal Clinical Nutrition, 5th ed.
- FEDIAF Nutritional Guidelines for Dogs and Cats (2021).
- Michell, A. R. (2005). Trace Elements in Small Animals. Vet Clin Small Anim.
- WSAVA Global Nutrition Toolkit (2021).
- AAFCO Official Publication.
