Immunity and athletes: What does the science say for immune balancing ingredients?

A fascinating new study published in Cell* shows how exercise triggers a multitude of internal responses, among them being responses by the immune system. The paper is described by the New York Times as the “most comprehensive cataloging to date of the molecular changes that occur during and after exercise and underscores how consequential activity — and inactivity — may be for our bodies and health”.

We’ve known for  years that exercise and immunity go hand-in-hand, and it’s not always beneficial. Moderate exercise promotes immune function, and individuals who exercise for one to two hours a day get 30-50% fewer infections than those who are very sedentary, according to Prof Mike Gleeson from Loughborough University in the UK.

Speaking to our European edition recently, Prof Gleeson explained: “This benefit is mostly thought to come from the increased 'immunosurveillance' effect. When you do exercise your heart rate increases and more blood is pumping through the body and this releases white blood cells that are the main part of the immune system and are normally stuck to the blood vessel walls.

"These white blood cells come into free flow and the white blood cell count increases by 10-100%. If you exercise for more than 40 to 60 minutes, this can cause an additional increase and this increased white blood cell count can last for several hours after the exercise.

“The cells in the blood present any foreign material they find in the blood as they get filtered through the lymph nodes. These lymph node cells are the cells that create an immune response to any infection trying to take hold in your body, so the greater that degree of blood flow the greater the degree of infection surveillance in your body.”

Too much of a good thing

However, excessive exercise – extreme endurance training, for example – is a physical stressor that has been shown to reduce key immune system components such as natural killer cells, neutrophils, T and B cells. Multiple studies have shown how people training for marathons or ultra-marathons are at an increased risk of upper respiratory tract infections (URTIs), for example.

So what are some of the ingredients that may help elite athletes’ immune function and reduce their risk of missing training days because of URTIs?

Probiotics

Probiotics are one area that are gaining a lot of traction. An international collaboration of sports nutrition experts worked together on the International Society of Sports Nutrition’s position paper on probiotics, and concluded: “Immune depression in athletes worsens with excessive training load, psychological stress, disturbed sleep, and environmental extremes, all of which can contribute to an increased risk of respiratory tract infections.

“In certain situations, including exposure to crowds, foreign travel and poor hygiene at home, and training or competition venues, athletes’ exposure to pathogens may be elevated leading to increased rates of infections.

“Approximately 70% of the immune system is located in the gut and probiotic supplementation has been shown to promote a healthy immune response. In an athletic population, specific probiotic strains can reduce the number of episodes, severity and duration of upper respiratory tract infections.”

Specific strains were highlighted by the authors for which there is human clinical data supporting a reduction in severity or duration of URTIs for endurance athletes, including Bifidobacterium animalis ssp. lactis Bl-04, Limosilactobacillus fermentum VRI-003 (PCC) (formerly Lactobacillus fermentum), Lacticaseibacillus casei Shirota (the ‘Yakult strain, formerly Lactobacillus casei Shirota), Lactobacillus helveticus Lafti L10.

Beta-glucan

Kerry’s Wellmune beta-glucan ingredient is also reported to confer immune benefits for marathon runners in human clinical trials. Wellmune is a beta 1,3/1,6 glucan ingredient derived from the cell walls of a proprietary strain of baker’s yeast (Saccharomyces cerevisiae) that reportedly ‘primes’ the innate immune system - the body’s first line of defense against invasion by bacteria and viruses.

Results of a study presented at the American College of Sports Medicine 59th Annual Meeting in 2012 indicated that two different forms of the beta-glucan ingredient - Wellmune soluble and Wellmune dispersible – were associated with 45% and 34% reductions in the number of days with URTI symptoms for 182 participants of the 2011 Austin Livestrong Marathon.

A 2018 study published in Journal of Dietary Supplements indicated that marathon runners consuming a beverage formulated with immune ingredient Wellmune saw a 19% reduction in the severity of upper respiratory tract infection (URTIs), compared to the placebo group.

In addition, runners missed fewer post-race workouts because of URTI and had a 10% decrease in total symptomatic days when they consumed the beverage with the beta-glucan-based ingredient for 45 days before and after a marathon, compared to the control group.

Vitamin C

The potential benefits of vitamin C for marathon runners may be one of the few instances of a nutrient’s efficacy in this specific population where support comes from a prestigious Cochrane Review.

Published in 2013, data from five trials with 598 marathon runners, skiers and soldiers on subarctic exercises indicated that the risk of common cold was reduced by 52% for vitamin C supplements of 0.2 g per day or more.

Harri Hemila from the University of Helsinki in Finland, and Elizabeth Chalker from Curtin, ACT in Australia explained that in the general population respiratory symptoms are usually linked to a virus, but for athletes may also be related to injury to the airways from heavy breathing that produce exercise-induced bronchoconstriction (EIB) symptoms.

“Thus the common cold studies of physically stressed people might have been measuring, at least in part, the effects of vitamin C on EIB instead of viral infections. Nevertheless, although the aetiology of symptoms is not clear in the physically stressed subgroup, the beneficial effect of vitamin C on acute respiratory symptoms in this subgroup is firm.”

Vitamin D

The potential immune benefits of the Sunshine Vitamin have been receiving a lot of attention in recent months as correlations are reported for vitamin D status and outcomes of COVID-19.

According to an extensive 2019 review by Prof Neil Walsh (School of Sport and Exercise Sciences at Liverpool John Moores University, England) in Sports Medicine, there is a “moderate-strong support” for the vitamin D for athlete immune health.

“It is widely accepted that vitamin D plays an important role in enhancing innate immunity via the induction of antimicrobial proteins; yet many of the actions of vitamin D on acquired immunity are anti-inflammatory in nature,” wrote prof Walsh.

“There has been growing interest in the benefits of supplementing vitamin D as studies report vitamin D insufficiency (circulating 25(OH)D < 50 nmol/L) in more than half of all athletes and military personnel tested during the winter, when skin sunlight ultraviolet B is negligible. The overwhelming evidence supports avoiding vitamin D deficiency (circulating 25(OH)D < 30 nmol/L) to maintain immunity and reduce the burden of URI in the general population, athletes and military personnel.

“A recent meta-analysis reported protective effects of oral vitamin D supplementation on respiratory infection (odds ratio 0.88); particularly in those deficient for vitamin D at baseline (odds ratio 0.30) and in those who received oral vitamin D daily or weekly, but not in those receiving one or more large boluses.”

Sports Medicine Vol. 49 (Suppl 2):S153–S168, doi: 10.1007/s40279-019-01160-3

Zinc

Zinc is another micronutrient that has been attracting interest in recent months. The potential immune health benefits of zinc are linked to “strong support” for treating the upper respiratory infections, notably the common cold, due to its anti-viral activity, said Prof Walsh.

A 2017 meta-analysis published in the Royal Society of Medicine’s JRSM Open found that zinc lozenges providing 75 mg per day of elemental zinc may shorten the duration of the common cold by about 33%, but the zinc must be taken within 24 hours of the onset of the infection.

On the other hand, Prof Walsh says there is “no support” for zinc to prevent upper respiratory infections. He also noted, “regular high-dose zinc supplementation can decrease immune function and should be avoided.”

Others

Limited support for a number of other nutritional interventions, including omega-3s, glutamine, echinacea, polyphenols like quercetin, and bovine colostrum, wrote Prof Walsh.

To conclude, Prof Walsh stated: “When considering nutritional supplementation, athletes must check the supplement comes from a reliable source and is tested by an established quality assurance programme.”

A shining light for the sports nutrition category

During the lockdowns and shelter in place orders introduced to tackle the spread of the coronavirus, sales of many dietary supplement segments surged, but one area that reportedly suffered was the sports nutrition category. But within sports nutrition – as in the wider supplements category, any product with an immune positioning is doing well.

Speaking during a recent webinar hosted by the European Specialist Sports Nutrition Alliance (ESSNA), Claudia Mucciardi, senior manager, regulatory affairs-EMEA for Glanbia Performance Nutrition, noted: “We’ve seen habits have changed in some ways and some haven’t. Protein has always been our best seller, and still is our best seller, but overall volumes have gone down.

“Performance and pre-workouts have gone down significantly, maybe because people don’t have the same intensity of workouts, they’re not at the gyms,” she added.

“We have seen a shift from the convenience-style products and ready-to-drink because convenience isn’t as big of a factor anymore and people have a lot more time on their hands, and it’s not a go-to to save time. But what we have seen that any sports nutrition supplement that has anything to do with immunity has remained strong.”

* Cell, 2020, Contrepois et al., Vol. 181, No. 5, pp. 1112-1130.E16, doi: 10.1016/j.cell.2020.04.043