The immune system acts to protect the host from infectious agents that exist in the environment (bacteria, viruses, fungi, parasites) and from other noxious insults. The immune system is constantly active, acting to discriminate ‘non-self’ from ‘self’. The immune system has two functional divisions: the innate and the acquired. Both components involve various blood-borne factors (complement, antibodies, cytokines) and cells. A number of methodologies exist to assess aspects of immune function; many of these rely upon studying cells in culture ex vivo.
There are large inter-individual variations in many immune functions even among the healthy. Genetics, age, gender, smoking habits, habitual levels of exercise, alcohol consumption, diet, stage in the female menstrual cycle, stress, history of infections and vaccinations, and early life experiences are likely to be important contributors to the observed variation.
While it is clear that individuals with immune responses significantly below ‘normal’ are more susceptible to infectious agents and exhibit increased infectious morbidity and mortality, it is not clear how the variation in immune function among healthy individuals relates to variation in susceptibility to infection.
Undernutrition leading to impairment of immune function can be due to insufficient intake of energy and macronutrients and/or due to deficiencies in specific micronutrients. Often these occur in combination. Nutrients that have been demonstrated (in either animal or human studies) to be required for the immune system to function efficiently include essential amino acids, the essential fatty
acid linoleic acid, vitamin A, folic acid, vitamin B6, vitamin B12, vitamin C, vitamin E, Zn, Cu, Fe and Se. Practically all forms of immunity may be affected by deficiencies in one or more of these nutrients. Animal and human studies have demonstrated that adding the deficient nutrient back to the diet can restore immune function and resistance to infection.1
Vitamin C is an essential dietary nutrient required as a co-factor for many enzymes, and humans are among the few animals that lack the ability to synthesize the compound from glucose. The reduced form of the vitamin, ascorbic acid, is an especially effective antioxidant owing to its high electron-donating power and ready conversion back to the active reduced form. Concentrations of the vitamin in body tissues and fluids are regulated through interactions of intestinal absorption, cellular transport, and excretion. The amount of vitamin C needed to prevent scurvy is very small and easily obtained in nearly all Western diets.
There is great interest in the clinical roles of vitamin C because of evidence that oxidative damage is a root cause of, or at least associated with, many diseases. However, these results may simply reflect a more healthful diet or lifestyle for individuals with a high vitamin C intake. The evidence that ascorbic acid acts as an important antioxidant in many body tissues is convincing. The new higher Recommended Dietary Allowance (RDA) for vitamin C of 75 mg for women and 90 mg for men is, for the first time, is based on the vitamin’s role as an antioxidant as well as protection
from deficiency. In healthy people, amounts greater than the RDA do not appear to be helpful. Vitamin C nutriture may be more important for people with certain diseases or conditions. High intakes of the vitamin are generally well tolerated; a Tolerable Upper Level was recently set at 2 g based on gastrointestinal upset that sometimes accompanies excessive intakes.2
Vitamin C concentrations in the plasma and leukocytes rapidly decline during infections and stress. Supplementation of vitamin C was found to improve components of the human immune system such as antimicrobial and natural killer cell activities, lymphocyte proliferation, chemotaxis, and delayed-type hypersensitivity.
Vitamin C contributes to maintaining the redox integrity of cells and thereby protects them against reactive oxygen species generated during the respiratory burst and in the inflammatory response. This is of special importance in populations in which insufficient intake of these nutrients is prevalent. In the developing world, this is the case in low- and middle-income countries, but also in subpopulations in industrialized countries, e.g. in the elderly.
A large number of randomized controlled intervention trials document that adequate intakes of vitamin C ameliorate symptoms and shorten the duration of respiratory tract infections including the common cold. Furthermore, vitamin C reduces the incidence and improve the outcome of pneumonia, malaria, and diarrhoea infections, especially in children in developing countries.3
The role of vitamin C in the prevention and treatment of the common cold has been a subject of controversy for 60 years, but is widely sold and used as both a preventive and therapeutic agent. So far over 60 studies have examined the effects of vitamin C on the common cold. There are studies reporting benefit. In three trials of subjects under heavy acute physical stress, common cold incidence decreased by on average 50%, and in four trials of British males common cold incidence decreased by on average 30% in the vitamin C groups. The dietary vitamin C intake in the UK is low, and consequently the benefit may be due to the correction of marginal deficiency, rather than high vitamin doses.
Regular vitamin C supplementation (≥1 g/day) has quite consistently reduced the duration of colds, but the size of the benefit has varied greatly. In the four largest studies the duration of colds was reduced only by 5%. In two of these studies, however, absence from school and work was reduced by 14-21% per episode, which may have practical importance. Three controlled studies recorded a reduction of at least 80% in the incidence of pneumonia in the vitamin C group, and one randomized trial reported substantial treatment benefit from vitamin C in elderly UK patients hospitalized with pneumonia or bronchitis.
It seems that the preventive effects of supplementation are mainly limited to subjects with low dietary vitamin C intake, but therapeutic effects may occur in wider population groups. The failure of vitamin C supplementation to reduce the incidence of colds in the
normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence suggests that it could be justified in people exposed to brief periods of severe physical exercise or cold environments.4,5
Pneumonia is one of the most common serious infections, causing two million deaths annually among young children in developing countries. In developed countries pneumonia is most significantly a problem of the elderly.
The prophylactic use of vitamin C to prevent pneumonia should be further investigated in populations who have high incidence of pneumonia, especially if dietary vitamin C intake is low. Similarly, the therapeutic effects of vitamin C should be studied especially in patients with low plasma vitamin C levels. The current evidence is too weak to advocate widespread prophylactic use of vitamin C to prevent pneumonia in the general population. However, therapeutic vitamin C supplementation may be reasonable for pneumonia patients who have low vitamin C plasma levels because its cost and risks are low.6
The growth, development and health conditions for children living under deprived conditions in developing countries are so adverse that immediate public health measures to reduce morbidity and improve nutrition are urgently needed.
The consumption by humans of part of the colostrum produced when a dairy animal gives birth is an established tradition in many traditional societies. Mammary fluids, colostrum and milk, deliver nature’s first host defense systems upon birth, and these essential liquids are critical for survival of the neonate.
Recent advances in food technology in industrial dairying allow for continuous availability of stabilized bovine colostrum concentrate, both natural and hyperimmunized against specific human pathogens. This is safe for the calves of the producers themselves, for laboratory animals, and generally for humans, with the caveat of the milk-allergic. Moreover, substantial amounts of orally ingested bovine colostrum concentrate survive their passage through the stomach to remain intact and active in the lower reaches of the bowel.7
The identification and characterization of anti-infectious proteins were among the early scientific discoveries and this group of proteins has long been recognized for promoting health benefits in both newborns and adults. Among the more widely studied are the immunoglobulins, lactoperoxidase, lysozyme, and lactoferrin. Recently, it was shown that alpha–lactalbumin may also function in a protective capacity dependent upon its folding state. Some of these, especially lactoferrin, also display an immunomodulatory role in which case a totally separate cascade of host defense responses is initiated.
Experts envision future contributions emerging from this research field as an opportunity to develop effective new therapies to be used in
treating infectious diseases and promoting health benefits in vivo.8 Studies in animals, human volunteers and naturally infected humans have demonstrated a therapeutic efficacy of oral bovine colostrum with certain infections. It is time to begin to assess the feasibility and potential effectiveness and efficiency of employing seasonal or chronic bovine colostrum feeding in populations of deprived infantile populations to reduce the rates of recurrent gastroenteritis and decrease immunostimulation to improve vitality and nutritional status in early life.
Bovine colostrum-based immune milk products have proven efficacy in prophylaxis and treatment against various infectious diseases in humans such as diarrheal diseases caused by various pathogens like E. coli and rotavirus. Bovine colostrum is used not only by calves, but also for the production of hyperimmunized colostrum, medicines or feed supplements. It has long been known that the consumption of bovine colostrum by humans has therapeutic effects e.g. in gastrointestinal infections, but only since the second half of the last century has it been possible to prepare stable, standardized preparations of colostrum. These biologics are administered to patients in combination with standard therapies as so-called balanced supportive diets.9
Oral ingestion of immunoglobulins in humans has been shown to be effective as prophylaxis against enteric infections. Experts treated children with rotavirus diarrhea with immunoglobulins extracted from immunized bovine colostrum (IIBC) containing high titers of antibodies against four rotavirus serotypes.
In this double blind placebo-controlled trial, 80 children with rotavirus diarrhoea were randomly assigned to receive orally either 10 g of IIBC (containing 3.6 g of antirotavirus antibodies) daily for 4 days or the same amount of a placebo preparation. The daily stool output (grams/kg/day), intake of oral rehydration solution (ml/kg/day), stool frequency (number of stools/day) and presence of rotavirus in stool were monitored for the 4 days during treatment.
Children who received IIBC had significantly less daily and total stool output and stool frequency and required a smaller amount of oral rehydration solution than did children who received placebo (P < 0.05). Clearance of rotavirus from the stool was also earlier in the IIBC group compared with the placebo group (mean day, 1.5 vs. 2.9, P < 0.001). No adverse reactions from the colostrum treatment were observed.
Treatment with antirotavirus immunoglobulin of bovine colostral origin is effective in the management of children with acute rotavirus diarrhoea.10