Download Immunity

Conclusion – Vits as ergogenic aids
• No ergogenic benefit vitamin supplementation
given an adequate diet.
– Except perhaps vit. E at altitude, C and multi B in hot
climates?
– Evidence exercise may increase req for riboflavin and
vit B6
– Those on poor diets/restricted energy/restricted food
groups – consider supplement
• Mega-doses (RDA x 10-1000) of vitamins may be
toxic, particularly the fat-sol.
– Hypervitaminosis A – case study adolescent footballer
(Fumich and Essig, 1983)
Dietary antioxidants and exercise
• Radicals - molecules that possess an unpaired
electron in outer shell/orbital
• Highly reactive and promote damaging oxidation
reactions with cellular proteins, lipids or DNA 
oxidative stress (impaired cellular function)
• Exercise results in increased production of radicals
(Davies et al., 1982)
• Primary source is mitochondria – 2-5% of oxygen
undergoes 1 electron reduction  superoxide
radicals
Antioxidants
• Cells protected by
– endogenous antioxidants eg. superoxide dismutase,
glutathione peroxidase and catalase;
– Exogenous dietary antioxidants eg. Vits E, C,
carotenoids, flavenoids, ubiquinones (eg. Coenzyme
Q)…
– Also trace minerals act as co-factors for antioxidant
enzymes eg. Cu, Zn, Fe, Se, Mn
– Nb Vits C and β-carotene can function as both anti- and
pro-oxidants
Antioxidant deficiencies and
performance
• Antioxidant deficiencies not widely reported in athletes
(Clarkson, 1995)
• Animal studies - antioxidant deficiency impairs performance;
• However Vit E deficiency in humans did not affect
performance (Bunnell et al., 1975)
• In contrast to animal studies antioxidant supplementation do
not enhance performance
– Except study at altitude where Vit E maintained anaerobic threshold
(Simon-Schnass and Pabst, 1988)
• Little evidence to recommend antioxidant supplementation to
enhance performance.
• – reduced IL-6 release from contracting muscle & thus cortisol
response
• Fischer et al. (2004) 4 weeks
combined supplementation with
vit C (500 mg/d) and vit E (400
IU/d) prior to a 3-h knee
extension exercise reduced
muscle IL-6 release systemic
rise in cortisol
• However, randomized doubleblind, placebo controlled study,
1500 mg/d vit C for 7 d before
ultramarathon race with vit C in
a CHO drink during the race
(subjects in the placebo group
consumed the same CHO drink
without added vit C) did not
affect oxidative stress, cytokine
or immune function measures
during and after the race.
Are athletes at increased risk of
oxidative stress?
• Training related oxidant stress  increases in enzymatic antioxidants
• However still see oxidative stress in highly adapted skeletal muscle
• If exercise  higher requirement of antioxidants – would expect
exercise to link via oxidative stress to morbidity
• Equivocal results as to levels of plasma antioxidants post-exercise; and
to effects of supplementation on exercise-induced oxidative stress.
– Vitamin E has been shown in some studies to decrease muscle damage.
E.g. supp with 400 iu vit. E and 200 mg vit C daily for 30 d reduced CK
concentrations following a marathon (Rokitski, et al. 1994; cited in Sen, et
al. 2000)
• High levels of antioxidants may blunt cellular adaptations induced by
exercise.
• Overall dietary supplementation with antioxidants cannot be
recommended at present time.
Immune Function
• Protects against, recognises, attacks and destroys
foreign elements
• Innate – natural and non-specific
– 1st line of defense
• Physical/structural barriers;
• Chemical barriers;
• Phagocytic cells and cytotoxic cells
• Acquired – adaptive and specific
– Monocytes/macrophages ingest, process and present
foreign material (antigens) to lymphocytes
– Proliferation of T- and B-lymphocytes which recognise
antigen if host is re-infected
Immunity and elite athletes
• Moderate exercise reduces risk of URTI cf. sedentary
(Matthews et al., 2002)
• Heavy training impairs immunity
– ↑susceptibility to infections, esp. URTI (Peters and Bateman, 1983;
Nieman et al., 1999)
– Not supported by all studies – no clinical confirmation of infection –
reported symptoms eg. Sore throat may be due to inflammation of
mucosal surfaces/inhalation dry air/pollutants.
– Post-exercise immune function is most depressed when exercise is
continuous, prolonged (>1.5hrs), of mod to high intensity (55 – 75%
VO2max) and performed without food intake.
– Periods of overreaching (intense training >1week) also depress immune
function (MacKinnon,2000)
– However
• Very few studies that show a link between exercise-induced immune
depression and increased incidence of illness in athletes.
Acute effects exercise and immunity
• Single bout prolonged, strenuous exercise
 temporary reduction in immune function
• Due to immunosuppressive actions of
adrenaline, cortisol;
– Muscle derived IL-6 appears partly responsible
for cortisol response to exercise
– Any factor affecting stress hormones (duration,
intensity, subject fitness) will affect immune
response
Nutrition and Immunity
• Prevalence/severity of infections are
increased by specific nutritional
deficiencies (Calder and Jackson, 2000);
– Prot, Fe, Zn, Cu, Se
• However….xs intake of individual
micronutrients can impair immune function
(ω-3 PUFAs, Fe, Zn, Vits A&E); excess Fe
can increase risk of infection.
Macronutrients
• Protein
– Inadequate protein intake impairs immunity (esp T
cells)
– Unlikely athletes would not reach extreme
protein/protein/energy malnutrition unless dieting
severely
– Those at risk:
•
•
•
•
Those restricting food to lose weight;
Vegetarians
Unbalanced diets (xs CHO)
Sports where leanness/low body mass, aesthetic sports, sports
Macronutrients
• Fat
– Little known re. fat and immune function;
– N-3 PUFAs may improve conditions associated
with overactive immune system e.g. rheumatoid
arthritis;
– High n-6:n-3 ratio may exert undesirable effect
on immune function during/post exercise (but
evidence lacking);
Macronutrients
• CHO
– CHO feeding during exercise attenuates rise in plasma IL6, catecholamines, GH, ACTH, cortisol;
– However
• inhibits lipolysis, and may attenuate the expression of metabolic
genes in the exercised muscle
• But may be argued that CHO intake during training allows athlete
to work harder/longer.
• No evidence that physiological adaptations are impaired by CHO
intake – is indicated that CHO is needed following periods of
intense training that temporarily induce overreaching
• CHO
Macronutrients
– Evidence CHO feeding for continuous strenuous exercise
(during, not before); but
– Magnitude of stress hormone response is higher in those
on very low CHO diets cf. normal/high CHO diets – preexercise glycogen levels imp;
– If train 2x/day – highest benefit when fed during exercise
(Li and Gleeson, 2005)
– Equivocal results for intermittent exercise (football (Bishop
et al.1999, 2002 rowing (Nieman et al.1999)
– Or when continuous prolonged exercise is performed to
point of fatigue (Bishop et al., 2001)
– Again evidence that CHO feeding  reduced incidence
URTI lacking. Trend for beneficial effect on post-race
URTI in study on 98 marathon runners (Nieman et al.,
2002)
Macronutrients
• Fluid
– Dehydration associated with increased stress
hormone response;
– Fluid prevents dehydration and maintains saliva
flow rate
– Saliva contains proteins with antimicrobial
properties, and saliva secretion usually decreases
during exercise
– CHO-containing drinks maintain saliva flow rates
(Bishop et al., 2002).
Micronutrients
• Minerals
– Isolated deficiencies rare (apart from Zn and Fe)
– Iron deficiency associated with increased morbidity from
infectious disease;
– Requirements may be higher in athletes due to losses in
sweat and urine;
– Excess Fe and Zn can impair immune function, & Fe can
increase susceptibility to infection
– Some evidence Zn can reduce symptoms/severity of
common cold – must be taken within 24 hrs of onset.
– Nb. Problems with Zn supps – nausea, taste, lowers HDL,
depressed immune cell function and reduces absorption Cu.
Micronutrients
• Vitamins
– Deficiencies of A, E, folic acid, B6, B12, C
impair immune function
– Such deficiencies need to be corrected.
– Some evidence A & E above normal levels in
very young/elderly enhance immunity (Calder
and Jackson, 2000)
– Megadoses of individual vits may impair
immunity, or have other toxic effects.
Micronutrients
• Vitamins contd.
– Peters et al. (1993) – 600mg
Vit C for 3 weeks prior to
90km untramarathon reduced
incidence of URTI cf.
placebo.
– Additionally 2 weeks postrace – lower incidence in
those with highest mean daily
intake of Vit C
– No effect additional fat sol
vits
– Due to reduced IL-6 release?
Other nutritional substances
• Glutamine
– Most abundant amino acid in plasma and
muscle
– Energy source for leukocytes
– Prolonged exercise associated with fall in
plasma [glutamine]
– Little evidence of benefits of supplementation;
– 1 study – Castell et al. (1996) – load postmarathon reduced incidence of URTI
Others
• No evidence BCAA’s, γ-carotone,
probiotics
• Echinacea
– Berg et al., (1998) – no athletes fell ill before
triathlon
– Turner et al., (2005) 437 volunteers exposed to
rhinovirus – NS effects.
– Very few good quality studies
Others
• Colostrum
– Shing et al., (2007)
• Colostrum suppressed post-exercise decrease in
immune parameters and  tendency towards
reduced URTI
– Crooks et al., (2006)
• Increase in salivary IgA in runners
– More studies warranted.
Summary on immunity
• Dietary deficiencies associated with depressed immune
function
• Adequate Fe, Zn, A, E, B6, B12 imp and protein
• Avoid exercising in CHO-depleted state, high CHO diet,
consume CHO-drinks during exercise (30-60g/hr)
• Routine megadoses ill advised – some can impair immune
function
• No evidence for immune boosting supplements –
particularly in athletes
• Some evidence high dose Vit C to reduce post-exercise
incidence of URTI
Refs
• Gleeson (2007) Immune function in sport and exercise J
Appl Physiol 103: 693 – 699
• Gleeson (2006) Can Nutrition limit exercise-induced
immunodepression? Nutrition Reviews 64(3): 119-222
• Nieman and Bishop (2006) Nutritional strategies to
counter stress to the immune system in athletes, with
special reference to football J Sports Sci 24(7): 763 – 772
• Williams et al.,. (2006) Antioxidant Requirements of
Endurance Athletes: Implications for Health Nutrition
Reviews 64(3):93-108