Studies performed with the Yeast β-glucan

Studies performed with the Yeast β-glucan preparation 

Feeding experiments with yeast β-glucans in rats showed that β-glucans increased the phagocytic activity of granulocytes and monocytes and the percentage of phagocytic cells. β-glucan feeding tended to have positive effects on the oxidative metabolism of these cell types. After stimulating monocytes with E. coli, the oxidative metabolism was significantly higher in the β-glucan group. Comparable effects were observed after phorbol myristate acetate (PMA) stimulation, a strong respiratory-burst stimulus

Application of the same orally applied insoluble β-glucan resulted in an increase in non-specific humoral immune parameters in rats as shown by higher lysozyme and ceruloplasmin activities and serum γ-globulin levels . This indicates that β-glucans may affect the synthesis of acute phase proteins. When the blood phagocytic cells were analyzed for their respiratory burst activity and their potential killing activity, the cells derived from the β-glucan fed group showed higher activity. Also, the proliferation rate of blood lymphocytes, when stimulated by Concanavalin A (ConA) or lipopolysaccharide (LPS), was higher in the β-glucan group, also indicating effects of β-glucans on cellular immunity .

These results were confirmed in another in vivo investigation in rats with cyclophosphamide suppressed immune systems . Under these conditions, feeding β-glucans led to an increased phagocytic activity of monocytes and granulocytes. Also, the respiratory-burst activity and the oxidative metabolism of granulocytes and monocytes stimulated with formyl-Methionyl-Leucyl-Phenylalanine (fMLP), PMA and E. coli was increased .

In a very recent investigation, the same β-glucan preparation from Spent Brewers’ Yeast was, for 42 days, fed to dogs suffering from Inflammatory Bowel Disease (IBD) . Within this time, the animals treated with β-glucan showed a significant improvement, measured by the Canine Inflammatory Bowel Disease Activity Index (CIBDAI). They further showed a decreased level of the pro-inflammatory IL-6 and an increase of the anti-inflammatory IL-10, as compared to untreated control animals .

From these experiments , it may be concluded that orally applied insoluble yeast β-glucans are able to strengthen a weakened immune system.

Susceptibility to common cold is related to a weak immune status or a weak defense system. In the early 1990s, Cohen and colleagues demonstrated that the immune status of people with a high susceptibility to common colds is affected by lifestyle factors such as stress, emotional imbalance, mood, specific vitamin deficiencies, or exposure to wet conditions and low temperatures, and that the susceptibility is correlated to the occurrence of cold infections . In contrast, a lower susceptibility to cold episodes reflects an improved defense against infections and, hence, a properly functioning immune system. Therefore, common cold is widely used as a proper model to investigate potential immune-modulating properties of natural substances, including β-glucans.

Two independent randomized, double-blind, placebo-controlled clinical trials showed that daily oral administration of the proprietary insoluble (1,3)-(1,6)-β-glucan, derived from brewers’ yeast, reduced the incidence of common cold episodes during the cold season in otherwise healthy subjects.

The results of the common cold studies in healthy adults showed the immune-stimulating effects of the same brewers’ yeast β-glucan preparation. As an immunomodulator, however, β-glucans are also able to induce anti-inflammatory abilities. showed an anti-inflammatory action of the same β-glucan preparation in overweight and obese subjects. Obesity is often associated with inflammatory conditions that lead to an activation of the innate immune system. Long-term activation of the immune system may cause several other health related problems, including insulin resistance . Indeed, yeast β-glucan consumption had an impact on immune function, as shown by an increase of both circulating levels and adipose tissue messenger RNA (mRNA) expression of the anti-inflammatory cytokine IL-10. Insulin sensitivity as well as circulating levels and mRNA expression of pro-inflammatory cytokines were, however, unaffected. The results indicate that intake of particulated yeast β-glucans also has anti-inflammatory properties.

These studies provide evidence on the potential immunomodulatory effects of yeast β-glucans: On one hand, the substances elicit/amplify (activate) the immune reaction as shown in the prevention of infections; on the other hand, they are capable of reducing the inflammatory reaction by inducing anti-inflammatory processes.

Clinical trials with other dietary yeast β-glucans

Similar results were obtained when healthy individuals (n = 79) received either 250 mg/day β-glucans or placebo over a period of 90 days during the peak upper respiratory tract infection (URTI) season. Even though there was no statistically significant difference in the total number of days with reported URTIs (β-glucans 198 days in 4.6%, versus 241 days in 5.5% in the control group, p = 0.06), the symptoms tended to be lesser in the β-glucan group. Of all assessed symptoms, only the item “ability to breathe easily” was significantly better in the β-glucan group than in the placebo group.

The ability to minimize post-exercise-induced immune suppression was measured in physically active subjects (n = 60), who consumed either 250 mg insoluble β-glucans or placebo (rice flour; cross-over design) for 10 days (pre-exercise supplementation period) before a bout of cycling. Blood analysis showed that ingestion of β-glucans significantly increases the total number of monocytes as well as of pro-inflammatory monocytes (p < 0.05). Further ex vivo LPS stimulation significantly increased plasma cytokine production of IL-2, Il-4, IL-5, and interferon-gamma .

Long-term stress is another factor known to weaken the immune system. When stressed women (n = 77) took insoluble bakers’ yeast β-glucan before breakfast for 12 weeks, they reported fewer upper respiratory tract symptoms compared to placebo (p < 0.05) and a better overall well-being (p < 0.05) . Similar results have been obtained in moderate to highly stressed subjects (n = 150; placebo n = 50; 250 mg β-glucan/day n = 50; 500 mg β-glucan/day n = 50) as well as healthy stressed subjects (screened for moderate level of psychological stress n = 122) . Once again, the subjects reported significantly fewer URTI symptoms and improved well-being (p < 0.05).

Although most of the trials mentioned above were underpowered and the differences in number of infections were not always significant compared to placebo, all are in support of the positive effects of insoluble β-glucans on the human immune system. The differences in the studies conducted with different β-glucan preparations may be explained by varying study conditions, sample size, study populations, applied dosages, and the different sources or isolation methods of β-glucan from brewers’ yeast or bakers’ yeast.

Conclusion

β-glucans from yeast are recognized by immune cells within the intestinal mucosa, amongst others by the dectin-1 receptor. Dectin-1 receptor activation induces several immune-stimulating effects important in the defense against invading pathogens. Furthermore, following uptake of β-glucans via dectin-1-stimulated phagocytosis, degradation processes within macrophages may make β-glucans systemically available.

However, not all β-glucan preparations have the potential to stimulate these reactions. In order to be able to activate the dectin-1 receptor cascade, β-glucans must comply with specific structural properties. It seems that insoluble, particulate (1,3)-β-glucans with 1,6-β-branches are able to activate this cascade, while soluble ones activate the antibody-mediated complement system via the CR3 receptor.