A vitamin deficiency will impair the healing of wounds. (Photo by marie b.)
I wrote a while ago that my wound healing has slowed down for some reason. It's nothing too dramatic, but small cuts and scratches don't seem to heal as fast as they used to.
In the previous post, I mentioned low zinc levels as a possible cause and decided to take 15 mg of zinc daily in addition to the 9 mg I get from my diet and multivitamin. Since I didn't see much of a difference with or without extra zinc, and because I'm not convinced that supplementing with zinc is necessarily a good idea, I stopped after a few weeks.
While I haven't injured myself lately to see if there's been a change, I've been doing some reading to know more about what effects wound healing. Recently, I found an old paper from 1955 titled Nutrition and Wound Healing (link). I know science moves on and everything, but since there's that certain something about old studies that I like, I decided to write a blog post about the paper.
It's probably no surprise that nutrition does have an effect on wound healing in humans and animals. The authors write:
It was shown in 1922 by Ebeling that a 10 per cent rise in the temperature of a cold-blooded animal would double the rate of wound healing. This indicates that wound healing is a chemical reaction. Thus, if the local factors discussed previously are kept at an optimum, the most important variable is the supply of the components for the chemical reaction. To accomplish this in the human being nutrition must be adequate.
By local factors, they mean things like bacteria, the amount of dead tissue and the vascularity of tissue to be repaired, which are not dependent on nutrition.
Wound healing and protein
So what is important when it comes to nutrition? Obviously, protein must play a role in the generation of new tissue. It seems like a reasonable assumption that a diet low in protein slows down wound healing. Conversely, a diet high in protein might be expected to speed up the wound healing process.
The authors mention a study from 1919 showing that animals on a high-protein diet had shorter healing times of surface wounds than animals on a high-fat, low-protein diet. Another study from 1935 showed that hypoproteinemia, a condition in which there's an abnormally low level of protein in the blood, resulted in poorly healing wounds in dogs. The reason was delayed formation of fibrous tissue and the accumulation of fluid beneath the skin. When proteins were reintroduced, the wounds healed normally. The same applies to humans:
Levenson and associates have presented numerous cases of healing burns in humans with a marked delay in healing being manifested in the hypoproteinemic patient.
It should be noted that protein intake by itself doesn't help much if some of the requisite amino acids are not present and protein synthesis cannot occur. Hence, there's a difference between consuming 100 grams of protein from eggs and consuming 100 grams of protein from beans.
There's no indication, however, that increasing protein intake above normal levels would further speed up wound healing. Since I eat either meat or fish daily as part of my semi-paleolithic diet, I don't think low protein levels are the issue in my case.
Wound healing and vitamins
What about vitamins? We know that vitamin D and vitamin A play a role in bone growth, so perhaps they are involved in the healing of wounds as well. According to the authors, the case is not clear cut:
In general, it appears that large doses of either vitamins A or D inhibit the healing of soft wounds in experimental animals. There is conflict as to whether small dosages are helpful. Bush and Lam feel that vitamin A will hasten the healing in vitamin A-deficient animals.
The same pattern rises again: fixing a deficiency will improve things, but increasing intake further won't do much good (and may even be harmful). The B-complex group of vitamin seems to fit into this category too, with rats deficient in pyridoxine (vitamin B6) and riboflavin (vitamin B2) showing impaired wound healing. Vitamin B12 has also been suggested to increase the strength of wounds in rats during the early healing period.
While vitamin C is necessary for building collagen and capillaries in healing wounds, it's not entirely clear how much vitamin C is optimal. Low levels of vitamin C are common among patients with wound disruption, and long-term depletion of vitamin C can halve the tensile strength of healing wounds. Yet, it takes more than a month of ascorbic acid depletion to see an effect. As the authors state, the data on vitamin C and wound healing is somewhat contradictory:
A similar interpretation might be made from the work of Carney, who observed no difference in the healing of war wounds of soldiers in the Italian campaign on vitamin C-deficient diets and low serum levels, compared to those on adequate diets and high serum levels. On the other hand, most surgeons have the feeling that wound healing is impaired proportionately to the degree of ascorbic acid deficiency.
There are no clinical reports on wound healing and disruption in patients alternately treated with large vitamin doses presently in vogue, compared to control to whom no additional vitamins were administered.
There are a couple of newer studies showing that ascorbid acid may improve wound healing when administered via injection, but studies on dietary vitamin C and wound healing are more scarce. One study on guinea pigs did suggest that increases in dietary ascorbic acid improved wound integrity (link).
Wound healing and other factors
An interesting point the authors mention is that the pH of wounds may play a role in wound healing. In lower organisms, the pH varies markedly from the regressive phase to the regenerative phase. Furthermore, animals on an acid diet were shown to have shortened wound healing times.
In my previous post, I wrote that intermittent fasting may be one reason for slower wound healing:
There is a paper (here) that says caloric restriction and intermittent fasting reduces cell proliferation in epidermal tissue, which would likely have an effect on wound healing as well.
In contrast, the authors quote studies on salamanders and rats showing that fasting accelerates wound healing, as long as they're not starved. Despite how fasting is defined here, it does seem to fly in the face of the study that says both CR and IF reduce cell proliferation in mice. Perhaps the severity of the wound is also important here.
A deficiency in protein or vitamins results in impaired wound healing, but increasing dietary protein or vitamin intake above normal levels does not necessary speed up wound healing. There are conflicting results as to whether fasting increases or decreases the speed of wound healing.
For more information on nutrition, protein and vitamins, see these posts:
Slowing Down Aging with Intermittent Protein Restriction
A High-Protein Diet Is Better than a High-Carbohydrate Diet for Weight Loss
Dietary Vitamin K2 May Reduce Prostate Cancer
Fish Oil Decreases Inflammatory and Atherogenic Gene Expression