Have you ever wondered if your exercise program makes you healthier or does it lead you to get more colds or sickness?
There is a lot of anecdotal evidence that after hard training cycles, marathons or periods of intensity or volume that the risk of getting an upper respiratory tract infection (URTI) goes up.
Regular moderate exercise keeps the risk of getting an URTI down much better then a person that has a sedentary lifestyle, but high intensity actually doubles the rate. (anecdotal)
There isn't a ton of research on this because many people don't report having a cold to their doctor. Self question profiles often ask people to remember if they have had a cold in the last 6 months. Sitting here writing this I can't recall if I have had one currently this year, but I know if I do get one, it feels like I just got over one. Ironic.
Some research demonstrates that the severity of the colds (days with it) go down with moderate intensity but no change on the frequency. One study demonstrates that running over 1388 miles in a year had a 3x more increase in URTI.
Open Window Theory: This states that the recovery period after exercise the immune system is suppressed giving pathogens a chance to gain a foothold.
High Intensity exercise does create a decrease in oxidative burst of neutrophils. This is not seen at moderate intensity. Natural Killer Cells has a decrease in activity around 2 hours into recovery. Lymphocytes as a whole have a decrease in below baseline 1 hour into recovery.
Carbohydrate research has shown that glucose ingestion retards the rise in cortisol and adrenaline but doesn't restore full immune function. It does show some improvement in post exercise immune suppression but no improvement in incidence of URTI.
Leukocytes use glutamine as an energy source as well as the carbs so it was hypothesized that supplementing with protein/glutamine should help. The glutamine part has been dismissed, but lack of protein in a diet has been shown to increase incidence of URTI. So athletes on a low calorie or restricted diet should be wary.
Fat has also been investigated. Exercise increases prostaglandins (PGE-2). This suppresses certain lymphocytes, natural killer cells and some cytokines. Things that drop after exercise. Studies have shown that when given anti-inflammatory drugs to stop PGE-2 the natural killer cells were restored to normal. This suggests that PGE-2 could be a big deal. One of the natural ways to block PGE-2 was with fish oil supplementation. This has been shown to work in the sense that NKC and some of the cytokines are improved in recovery. There hasn't been much research to see if this actually improves the incidence of URTI's though.
If exercise stays the same and the diet is dropped from 40-50% percent to 25-30% percent fat the persons lymphocytes and NKC activity is enhanced. (What I don't know is what the carb levels/protein levels were with the high fat. High fat/high protein low carb, I believe would be much different then high fat, high carb, low protein.)
One cool supplement worth mentioning is Quercetin. 12 weeks supplementing with this reduced the number and frequency of sick days in middle aged through elderly volunteers. Capers have the highest quercetin values in a food. I believe there are a few companies that sell a sports drink with quercetin as the main antioxidant.
Probiotics have been shown to potentially have a 50% reduction in the number of URTI's and improvements in the ability to train when URTI's are present. They say 80-90% of our immune function runs through our "gut's" so this makes sense.
In summary, I would recommend a diet that is high in protein includes fermented foods, fat is within the percentages and fish oil and probiotics are supplemented with.