What is It?

Vitamin C is considered a non-essential nutrient for dogs and is water soluble. Because of de novo synthesis, dogs do not require this nutrient to be provided in their diet. If you have been around Raw Fed & Nerdy for some time, surely you have heard that not essential does not equate to not beneficial.

Vitamin C is synthesized from glucose in the liver or kidneys and under normal circumstances, dogs will not have a vitamin C deficiency. Certainly, conditions such as starvation where the materials are not there to synthesize vitamin C would mean a vitamin C deficiency (among many other deficiencies).

Vitamin C is very fragile. Exposure to oxygen can destroy it- as can heat. Vitamin C is stable as a dry powder. Stability is also reasonable in an acidic environment.

Is it Beneficial?

Because dogs are able to synthesize vitamin C, it is reasonable to wonder if a dietary supply of vitamin C is beneficial. Keep in mind that dogs (and cats) have a reduced ability to synthesize vitamin C compared to other mammals. 

During times of high stress, there is a potential that dogs are unable to synthesize optimal amounts of vitamin C even though they are able to increase production in the response to injury.

Conditions that may benefit from dietary vitamin C include chronic kidney disease, arthritis (particularly age related), during times when the dog is fighting an infection, and because older dogs can have disturbances to their ability to synthesize non-essential nutrients (glycine is another example), vitamin C can be beneficial there as well.

Canine athletes are also often supplemented with vitamin C (as well as increased levels of PUFAs as n-3 and vitamin E).

However, not every dog should have increased amounts of vitamin C. Vitamin C is relatively safe (though any condition, particularly cancer, you should check with your vet).  Vitamin C can easily cause digestive upset in dogs.

How Much?

There is no recommended allowance for vitamin C per NRC (or any nutrient guideline) because it is non-essential. Vitamin C regenerates vitamin E at a 1:1 molar ratio and this ratio is used in clinical textbooks to provide a starting dose of vitamin C for dogs. When formulating, you could use a vitamin E to C ratio of 3:1 (note: it is not a 1:1 ratio on a mg basis, only a molar basis).

Simply put, if you have 3 mg of vitamin E, you would add 1 mg of vitamin C.

You don’t really need to overthink it. Therapeutic diets often go higher and work with specific amounts depending on the condition, but for adult, healthy dogs, inclusion of fresh fruits and veggies will boost vitamin C. Because dogs synthesize C, you don’t need to sweat it.

Also, keep in mind that most people over supplement vitamin E and so a 3:1 ratio may be too much vitamin C for the dog’s gut to tolerate or may provide an amount of C that is not longer beneficial and is excreted. Always start slow and work up.

How This Experiment Works

Recall vitamin C’s role as an antioxidant. Vitamin C is oxidized by Iodine. When we run out of vitamin C, or when the vitamin C is spent, the excess Iodine that has not reacted with vitamin C will react with the starch (the starch is added to the tea during the experiment) and the tea turns blackish blue.

By calculating how much Iodine is needed to oxidize 1 mg of vitamin C, we can calculate how much vitamin C is in the tea samples by recording how much Iodine it takes before the tea turns black/blue.

HCl is also used as a catalyst.

Notice how we can add iodine to the tea sample and swirl it- it disappears. Eventually it does not when you add enough, which indicates that all the vitamin C is spent.

Vitamin C has been oxidized.

I won’t bore you with the full lab write-up- so here is the tl;dr version.

I filled two glass containers with 200 grams of RO water, each. In one I used one bag of a commercial brand Traditional Medicinals  Rosehip/Hibiscus tea. I did this because somebody wanted to know if that particular tea had any vitamin C. Spoiler alert, it didn’t. Not for any preparation method. So I am not really going to discuss it much. Boooo.

In the other glass container, I used 10 grams (about 1 tablespoon) of Mountain Rose Herbs dried rosehips.

The Containers were covered and placed in the fridge overnight for about 9 hours (which may be a little long for a lighter tea cold brew).

The next day, 2 more glass containers were prepared using the same amount of water (200 grams). The water was heated until boiling and then let sit for about a minute. 10 grams of the rosehips were used in one and 1 bag of the other major disappointment of a tea was used. The teas were allowed to steep for about 5 minutes before removing.

Different volumes of each tea was tested, again starch, Iodine, HCl, and RO water was used in the experiment. Iodine was added until I noticed even a slight darker note of the tea, just to be conservative.

Tl;Dr The tea was prepared with 200 grams of water. Cold brew sat for 9 hours overnight and the hot brew sat for 5 minutes. The experiment was done and the results are reported in the above table. 

How Much Vitamin C?

The specific amount of vitamin C is listed in the table above- about 80 mg of C for cold brew and 50 mg when using hot water (This is per 200 g of water using 10 g of rosehips). However, to put it in perspective: Basically, its probably safe to assume that the high quality rosehips from mountain rose herbs provides appreciable amounts of vitamin C for hot and cold brewing methods. Cold brewing resulted in much more vitamin C (about 40% more), but a quick hot brew still provided as much vitamin C as a small orange. Not bad! Not to mention that tea has other good stuff in it, too.

Because some dogs don’t like plant matter and citris fruits are often not well-tolerated, sharing some of your rosehip tea could certainly be beneficial. A vitamin C supplement works, too. 😉

You might be wondering what happened with the hot brew analysis for trial one with 10 mL. No idea. But I did all of them twice except the 10 mL so I probably messed up the 10 mL sample somehow. 

Sourcing

Like many other plants, lots of factors affect the amount of vitamin C that may be in a plant- including altitude. Therefore, there are going to be differences in nutrient content in the rosehips that you buy tomorrow and the ones you get in a few months from now. The ones from Mountain Rose Herbs are said to be Rosa canina and Rosa rubiginosa. These tend to fare well with vitamin C content. Other kinds of rosehips can have higher or lower amounts of vitamin C.