malmo, I have seen for over a decade now that you are loathe to be contradicted and you condescend to anyone less than a current or former national record holder. Neverthless, cross country skiers (not just local yokel schlubs but Olympic level athletes and coaches) have long held the belief that there is a relationship between high volume training, nutritive depletion, and immunity.
Here are a couple of sources one technical, the other non-technical by a nurse for popular audiences:
Immunological effects of competitive versus recreational sports in cross-country skiing.
Mueller O, Villiger B, O'Callaghan B, Simon HU.
http://www.ncbi.nlm.nih.gov/pubmed/11258642University Hospital, Department of Rheumatology, Zuerich, Switzerland.
olaf.mueller@ruz.usz.chAbstract
For a period of two months during the competitive season the effects of endurance training in cross-country skiers were evaluated in order to compare the adaptive and innate immune systems between 10 competitive athletes, 10 moderately trained athletes and 10 untrained healthy controls. The main results were as follows: the peripheral T-lymphocyte count of the competitive athletes was decreased. In contrast the number of peripheral blood NK cells was increased in this group. These data imply a diminution of the adaptive immune system due to repeated bouts of intense exercise and contemporaneous reinforcement of the innate immune response. Moreover the inducible IL-12-expression following monocyte stimulation was significantly decreased in competitive athletes. Compared with the other two groups, the moderately trained athletes showed a significantly increased production of IFN-gamma upon T-cell stimulation. These data suggest that the immune system may profit from moderate endurance training by an increased capacity to generate IFN-gamma while the immune situation following repeated exhausting exercise of competitive athletes tends to deteriorate through downregulation of IFN-gamma and IL-12.
http://www.masterskier.com/article.asp?aid=167