Week 5 (1) - Nutrition and immune function Flashcards
Immunity defintions:
“the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells…”
“Immunity is your body’s ability to recognise germs to prevent them from causing illness. The immune systems job is to help identify and eliminate dangerous germs that enter the body before they can cause disease or damage”
The immune system is surveillance system that seeks out germs/ pathogens to prevent them causing harm (illness/infections) to the body
Several factors that affect immunity in athletes:
- Exposure to pathogens (this is the biggest determinant)
- Environmental stress – e.g., heat, cold
- Physiological stress – exercise is a physiological stress on the body
- Poor diet
- Psychological stress – e.g., nerves, anxiety
Exercise and immunity (the physiological stress):
- Exercise is a physiological stress – when you perform intense exercise (E..g, marathon – prolonged and strenuous), it can cause a transient immune suppression – after the event you are vulnerable to getting ill
- Greatest in prolonged, strenuous exercise
Nieman et al 1993- the number of immune cells available to fight off pathogens and protect us in the 2 hours after exercise:
Immediately post exercise you get a rapid increase in immune cells needed to fight infection
1-2hours post exercise there is a dramatic increase in these immune cells, before they return to resting levels.
An open window a few hours after exercise where you are more vulnerable
*Lytic = NCKs
The debate remains about whether physiological changes (and exercise per se) decreases immune function – could just be the redistribution of key immune cells to other tissues and non-exercise factors.
- The decrease in immune cells is likely to just be a distribution in immune cells – they have gone to other tissues such as muscles
- Other non-exercise factors may be a bigger cause of the evident exercise induced immune suppression
Innate immunity
Example cells involved: Dendritic cell, IL C2, Macrophage, mast cell, neutrophil, NK cell, B-1 cell, IRA B cell, NKT cell
- These cells rely heavily on glucose to function (CHOs)
- It includes physical barriers, such as skin and mucous membranes, and special cells and proteins that can recognize and kill germs.
- The problem with these special cells and proteins is that they can kill a germ, but once the germ is dead, the innate immune system forgets it. It does not communicate any information about the germ to the rest of the body. Without this information, the body cannot prepare itself to fight this germ if it should reinfect the body
Adaptive immunity:
Example cells involved: CD4 T cell, CD8 T cell, Treg cell, B-2 cell, NKT cell
Immunity is created in response to exposure to a foreign substance. It can use memory of previous exposure to eliminate pathogens.
- It takes about 14 days for your body to make antibodies
- Antibody production is one of the most important ways that immunity is developed.
- 2 types of adaptive immunity:
1) Active immunity: antibodies that develop in a person’s own immune system after the body is exposed to an antigen through a disease or when you get an immunization (i.e. a flu shot). This type of immunity lasts for a long time
2) Passive immunity: antibodies given to a person to prevent disease or to treat disease after the body is exposed to an antigen. Passive immunity is given from mother to child through the placenta before birth, and through breast milk after birth. It can also be given medically through blood products that contain antibodies, such as immune globulin. This type of immunity is fast acting but lasts only a few weeks or months
Low CHO diets increase stress hormone response
- Asked individuals to run for 1hour at 60% vo2 max
- Cortisol decreases immune activation – decreases body’s ability to fight against pathogens
- Cortisol increased after low CHO diet – increased stress hormone response)
- Another interesting property of cortisol is that it acts as an anti-inflammatory signal, meaning that it acts as an “off switch” for your immune system, helping prevent the inflammatory response described earlier
Can drinking CHO during exercise help?
In theory: CHO consumption maintains plasma glucose. This decreases stress hormone response e.g., cortisol which boosts immune system.
In practice: - Asked to perform 3 hours of cycling exercise and measured IL-Ra (pro-inflammatory cytokine). When no CHOs were consumed, pro-inflammatory cytokines were increased post exercise (inflammation was higher)
Dehydration:
The belief held by some exercise immunologists is that dehydration may impair immune health of athletes as dehydration increases physiological strain and immunomodulatory stress hormones
Evidence suggests that modest dehydration typically experienced by athletes has relatively limited impact on exercise immune response.
* For example, recent research shows that modest dehydration (~4% body mass loss) caused by fluid restriction and prolonged moderate-intensity exercise did not affect circulating antigen-stimulated cytokine production, tear fluid IgA or saliva antimicrobial responses, including IgA, lysozyme and lactoferrin.
Leukendrup and Gleeson found that neutrophil degranulation (want it to be higher post exercise) was decrease after exercise when the athlete was dehydrated. Dehydration may affect immunity – but how well this translates to illness is poorly understood
Fats:
- Very rarely do we supplement with fats due to their poor digestibility (takes 6hours to digest fats – CHOs are quicker to digest)
- Less is known about the role of a high fat diet on exercise induced immune function
- Having a high fat diet cold compromise CHO intake
- Having a low-fat diet can lead to deficient intake of important fat soluble vitamins e.g., vit A, DE, E and K
Several immune cells are affected by low protein intake:
- They are more important in adaptive immunity e.g., for T cells
- Has especially negative effects on T-cell function
The important role of the amino acid glutamine:
- Glutamine is an important energy source for both the innate & adaptive immune system (especially leukocytes)
- Glutamine can be bought as a powder form – it is often found in protein powders
- Levels seem to rise during short duration HI exercise but fall during prolonged LI exercise
Glutamine falls after exercise – intensity dependant:
- Research measured plasma glutamine concentrations after HI exercise to exhaustion (around 40 mins long) vs exercise that was 3 hours long
- Glutamine dropped more during the 3hr session
Role of glutamine in infections:
- Took plasma glutamine samples from Olympic athletes and categorised them
- Those without an infection had higher glutamine levels than those who did have an infection
- Glutamine lower in those reporting an infection and acute fatigue and chronic fatigue (or overtraining syndrome).
