- Trial 1: Mean iron absorption from the drink with 109 CFU of L. plantarum was 28.6% compared to 18.5% for the control drink
- Trial 2: Mean iron absorption from the drink with 1010 CFU of L. plantarum was 29.1% compared to 20.1% for the control drink
The average iron absorption was 28.8% with L. plantarum when the absorption values for all subjects were combined, which was significantly higher than the iron absorption of 19.3% with the control drink. The study found iron absorption was 50% higher with non-heme iron from a fruit drink with L. plantarum than a similar fruit drink without the probiotic.
Details of the mechanisms by which probiotics can increase iron absorption are lacking. It is suggested that some Lactobacillus strains can increase the bioavailability of iron because they have the phytase enzyme that can break down phytates during fermentation. Yet, L. plantarum has minimal phytase activity and the amount of phytates was low in the fruit drinks in the study. Enhanced iron absorption may be the result of the strain’s ability to colonize the gut and increase mucin (the main component of the mucus layer that lines the gut) excretion. It is suggested mucins can bind to iron and prevent iron removal. Also, mucin may increase iron uptake because of its effect on iron transport proteins that bring iron into cells. Finally, another possible mechanism may result from the decrease in gut pH because of Lactobacilli growth. This creates a more acidic environment to change the iron (i.e., ferric iron) to a more absorbable form (i.e., ferrous iron).
Enhance Vitamin D Absorption
Vitamin D is critical for bone health, maintaining phosphate and calcium homeostasis – and maybe for physical performance. Yet, vitamin D levels are very low, with the greatest effects based on geographic location (e.g., northern latitude), season of the year and skin color. Even fortified vitamin D milk is not sufficient enough to prevent vitamin D deficiency for all adults at every time of the year. It is suggested that athletes, compared to the general population, may be more susceptible to vitamin D deficiency, and possibly because of inflammation, muscle damage, increased immune activity and increased protein synthesis.
Before we delve into the research highlighting vitamin D-boosting probiotics, the importance of vitamin D for athletes requires emphasizing complications of vitamin D deficiency and the prevalence of vitamin D deficiency among athletes.
These precursors are transformed in the liver and kidneys to:
- 25-hydroxyvitamin D (25(OH)D): the inactive storage form
- 1,25-dihydroxyvitamin D (1,25(OH)2D): the biologically active form under tight regulation in the body
1,25-dihydroxyvitamin D interacts with vitamin D receptors found in every tissue of the body. This includes skeletal muscle, which suggests the important effect vitamin D may have on skeletal muscle.
The best indicator of vitamin D status is reduced blood levels of 25-hydroxyvitamin D [25(OH)D]. The three categories of vitamin D status based on serum 25(OH)D are:
- Risk of deficiency: <30 nmol/L
- Risk of inadequacy: 30-49 nmol/L
- Sufficiency: 50-125 nmol/L
Low levels of vitamin D are prevalent in the general population. A low level is also a risk factor for: osteoporosis, cardiovascular disease, type 2 diabetes, and cancer. Vitamin D deficiency is also associated with depression, cognitive decline and neurological complications. More specific to athletic performance, vitamin D deficiency also may break down muscle and result in muscle weakness.
A few studies have suggested that a lower vitamin D intake may be associated with microbiome changes.,
A 2015 systematic-review and meta-analysis of 23 studies and ~2,300 athletes found that 56% of athletes had inadequate vitamin D levels.
A recent cohort study assessed vitamin D levels in 80 professional NFL players (the Pittsburg Steelers) and its association with race, history of broken bones and staying on the team during the 2011 offseason.
- Mean vitamin D level was 27.4±11.7 ng/mL
- Significantly lower levels for black players, which was 84% of the team, (25.6±11.3 ng/mL) compared to white players (37.4±8.6 ng/mL)
- All athletes with vitamin D deficiency (<20 ng/mL) were black
- 91% of athletes with vitamin D insufficiency (20-32 ng/mL) were black
- 68.8% of the team had vitamin D levels lower than 32 ng/mL
The associated results:
- Vitamin D levels were much lower in players who had at least one bone fracture compared to players who had no fractures
- Players who were cut during the preseason as a result of injury or poor performance had significantly lower vitamin D levels compared to players who stayed for the regular season
Ultimately, athletes with vitamin D levels above 32 ng/mL played in more seasons than athletes with vitamin D deficiency. Vitamin D deficiency and insufficiency were prevalent among football players, especially black players. Those with a lower the vitamin D level had a higher risk for getting cut.
These results suggest the need to optimize vitamin D not just for NFL players, especially black players, but potentially all athletes. To address vitamin D deficiency, probiotics is an attractive nutritional intervention.
Jones, Martoni and Prakash published the first human data on probiotics increasing vitamin D absorption in humans. The randomized controlled trial found the probiotic strain L. reuteri may increase serum 25-hydroxyvitamin D by 25.5%.
The participants’ two-day dietary intake was measured at weeks 0 and 9 to evaluate calories, lipids, proteins, carbohydrates, vitamin A, retinol, carotenoids, vitamin E and vitamin D.
The study primarily measured the change in serum low-density lipoprotein-cholesterol (LDL-C) over the nine weeks. Fat-soluble vitamin analysis was conducted for weeks 0 and 9 following the intervention.
- L. reuteri increased serum 25-hydroxyvitamin D by 14.9 nmol/L (25.5%) – a significant difference compared to placebo, which was 17.1 nmol/L (22.4%)
- No differences in the absorption of other fat-soluble vitamins
Currently, this is the first study to show a probiotic supplement increased vitamin D levels. However, the mechanism is unclear. It may be the result of 1) an increase in vitamin D absorption or 2) greater synthesis of the vitamin D precursor. Yet, influencing the microbiome with the right probiotics signals a feasible approach to increase vitamin D.
Alleviate Symptoms of Lactose Intolerance
Dealing with lactose (i.e., the natural sugar in milk) intolerance as an athlete is frustrating, especially for those who want to use the fluid, protein and carbohydrate in milk or products with whey protein for recovery. Lactose intolerance results from a low amount of the lactose cleaving-enzyme β-galactosidase (i.e., lactase) in the mucosal layer of the small intestine. Secondary causes of lactose malabsorption result from other health complications (which can be reversible) including:
- Inflammation of the small intestine
- Protein-energy malnutrition (i.e., lack of protein)
Probiotics that have high β-galactosidase activity may help those who are lactose intolerant. This is why those who are lactose intolerant may be able to tolerate yogurt because the lactose is already partially broken down.
A randomized controlled trial investigated the effect of L. reuteri supplementation, compared to placebo, on symptoms of lactose intolerance in lactose intolerant people randomly assigned to one of three 20-subject treatment groups: tilactase (e.g., Lactaid) group, placebo group and L. reuteri group. Lactose maldigestion was assessed with the hydrogen breath test and GI distress symptoms. The study found that L. reuteri, compared to placebo, lowered the amount of excreted hydrogen and reduced GI symptoms following lactose intake.
Microbial β-galactosidase (also found in L. bulgaricus and Streptococcus thermophilus) may be an effective treatment to alleviate lactose intolerance symptom for lactose malabsorbers. In fact, the bacteria don’t need to be alive – just the cell walls need to be intact to protect the enzyme when it passes through the stomach. Lactose digestion may improve because the passage of lactose through the gut is delayed, which allows β-galactosidase more time to breakdown lactose.
Enhance the Conversion of Nitrate from Beetroot Juice to Nitric Oxide
Beetroot juice is the latest in functional foods for sport performance. The dietary nitrates in beetroot juice convert to nitric oxide (NO), a molecule that widens blood vessels and allows nutrients and oxygen to enter skeletal muscle. NO increases efficiency of oxygen use in muscles during strenuous exercise. The entero-salivary nitrate-nitrite-NO pathway (i.e., GI system) starts with conversion of dietary nitrate to nitrite in the mouth, then the stomach and finally the small intestine. Yet, the link in the conversion of nitrates to NO requires good bacteria throughout the entire GI tract.
Bacteria on the tongue that convert nitrate to NO (by using the enzyme nitrate reductase) can be destroyed by antibacterial mouthwash. Govoni et al. used seven healthy volunteers to investigate what impacts the ability of oral bacteria to metabolize inorganic nitrate to form nitrite and then bioactive NO. Notably, the bacteria in our mouth that convert nitrate to NO were destroyed by antibacterial mouthwash, which led to a lack of NO and no benefits from beetroot juice nitrates.
Beetroot juice (or other food containing dietary nitrate) is not the only way to generate NO. Our body can produce NO from the amino acid L-arginine and oxygen by using the enzyme nitric oxide synthase. This endogenous way of producing NO greatly impacts the GI tract.
To address this, a study investigated if specific gut bacteria, in humans and in rats, could produce NO. Fecal samples from eight healthy volunteers were used to measure the NO production by different bacteria. Lactobacilli and Bifidobacteria in human feces generated NO from nitrite, and a few of the bacteria strains generated NO from nitrate. Rats receiving Lactobacilli supplementation with nitrate present produced more NO in the gut than rats with no gut bacteria.