How Cyclists Can Strengthen Immunity This Winter: Part Two.

The average duration of the common cold is 7.4 days, where 25% of cases can last up to 2 weeks. Through an athlete's eyes, reducing the time missed from training or competition through illness is always a welcomed sign.

In part 1, we identified that nutrition status has a marked impact on immunity and, therefore, your ability to fight illness and infection.

This week, we cover proposed nutrients and supplements to improve immune resistance.

Immune resistance is the immune weaponry that protects us by destroying viruses, pathogens and microbes.

Immune tolerance, which we'll cover in part 3, are the nutrients and supplements to improve immune tolerance, i.e. our ability to endure and control infection.

A recent review by Walsh (2019) examined the effect of frequently used supplements and nutrients that are proposed to offer an immune resistance benefit in preventing upper respiratory infections (URI) in athletes.

The frequently used supplements proposed to support immunity in athletes are:

𝟭) 𝗭𝗶𝗻𝗰 Tablets/capsules/pills/food

Potential = Zinc deficiency results in impaired immunity. Zinc is required for DNA synthesis and functioning of immune cells.

Supplement Benefit = No support for preventing URI. Regular high-dose supplements can decrease immunity and should be avoided. Therefore, correcting zinc deficiencies would be very beneficial, but there's little need for elevated amounts.

2) Zinc lozenges

A 2014 Cochrane review by Singh and Das investigated the efficacy of zinc lozenge supplementation in reducing the frequency, severity and duration of the common cold.

Based on their analysis, they found that zinc lozenge supplementation, when administered 24 hours of the onset of symptoms (in otherwise healthy individuals):

 1) Was associated with a significant reduction in the duration of illness.

 2) It made individuals less symptomatic after seven days vs. a placebo.

 3) Reduced incidence rate ratio (IRR) and school absence would hypothetically accelerate the return to full training.

 4) Was not associated with the severity of illness.

Interestingly, the delivery method/formulation is of high importance.

Zinc lozenges, not as a syrup or tablet at a dose of ≥ 75 mg/day, appear to be most effective when taken on the onset of illness due to their ability to inhibit the replication of the common cold virus in the pharyngeal region.

Note that the zinc from the lozenges fights against viruses at the local level (throat, nose, etc.) and does not offer a benefit through changing zinc levels in the blood. This differentiates the effectiveness of zinc lozenges and zinc obtained through diet and tablet-based supplementation.

3) 𝗚𝗹𝘂𝘁𝗮𝗺𝗶𝗻𝗲:

Potential = Acts as an energy source for immune cells (lymphocytes), and circulating levels are lower after heavy training.

Supplement Benefit = Supplementing before and after exercise does not alter immune function. However, there's some evidence for reduced URI incidence after endurance events through daily supplementation.

4) Formulated Sports Products (carbohydrate drinks and gels):

Potential = Maintains blood glucose during exercise, lowers stress hormones and counters immune dysfunction.

Supplement Benefit = Limited support that consuming 30-60g carbs/hour during exercise reduces infection risk. Carbohydrates can dampen stress hormones, but no meaningful changes in immune function.

5) 𝗕𝗼𝘃𝗶𝗻𝗲 𝗖𝗼𝗹𝗼𝘀𝘁𝗿𝘂𝗺:

Potential = Claimed to improve mucosal immunity and improve resistance to infection – contains antibodies, cytokines and growth factors.

Supplement Benefit = Limited support showing a decreased incidence of URI from maintaining mucosal immunity after heavy exercise.

6) β-𝗚𝗹𝘂𝗰𝗮𝗻𝘀:

Potential = Found in yeast, fungi, algae and oats cell walls: Claimed to stimulate innate immunity.

Supplement Benefit = Effective in mice with the influenza virus; however, studies with athletes show no benefit to immunity and mixed results for URI incidence.

7) 𝗘𝗰𝗵𝗶𝗻𝗮𝗰𝗲𝗮:

Mechanism = Herbal extract claimed to enhance immunity through enhancing macrophage function (detecting, engulfing and destroying pathogens).

Supplement Benefit = Meta-analysis shows a slight reduction in URI incidence but no influence on duration in the general population. There are unclear findings in athletes; more research is needed.

8) 𝗖𝗮𝗳𝗳𝗲𝗶𝗻𝗲:

Mechanism = Immune cells express receptors that caffeine can bind to.

Supplement Benefit = There's evidence that caffeine can activate lymphocytes and reduce the decline in neutrophil function after exercise. There is no known evidence for reducing URI in athletes.

Long story short, the only supplement with strong evidence to enhance our immune weaponry is zinc lozenges.

In addition, the most beneficial nutrition intervention to maintain immune function is not being deficient in nutrients. Eating various foods or potentially supplementing with specific nutrients is recommended to ensure sufficiency. Beyond this, nutrient amounts greater than the recommendations most likely offer zero benefit and, in some cases, could impair immunity.

Ultimately, the common 'immune boosters' advertised on the TV or down the supplement aisle in supermarkets don't offer a great deal in shielding us from infection.

In part 3, we examine the putative benefits of nutrients and supplements that improve immune tolerance: probiotics, vitamins C, D, E, omega 3s, and polyphenols.

- Coach Chris