An Update on Probiotic Safety and Efficacy

Probiotics are live microorganisms that have recently gained popularity for being beneficial to human health and digestion. There are several forms of probiotics, perhaps the more widely used form is the lactic acid producer. Studies with the strongest clinical evidence have shown beneficial effects of probiotics for acute infectious diarrhea in children, antibiotic-associated diarrhea, among several others. Some studies have shown promising prophylactic effects for necrotizing enterocolitis, the common cold, irritable bowel syndrome, cancer, mucosal immunity, allergies, and urinary tract infections. While probiotics are generally known to be safe, there are occasional reports of adverse effects. Chief among the safety concerns is the ability of these organisms to invade the blood stream causing bacteremia or fungemia. Another concern relates to modifying the gut immune system, the largest immune organ, at a young age if probiotics are given to infants. With regards to lactic acid-producing probiotics, there is concern that accumulation of lactic acid in the body and the development of lactic acidosis can cause clinically significant problems. This article will provide an update on the safety and efficacy of probiotics and summarize the current literature about probiotics, including the issue of quality control. HISTORY AND OVERVIEW Fermented foods and cultured milk have been used by humans for many centuries. The first written scientific report was not until 1908 when the Nobel Prize Russian scientist Elie Metchnikoff made observations that human health and longevity were associated with the ingestion of lactic acid-producing bacteria. He noted that Bulgarian peasants who consumed large quantities of sour milk containing the bacteria now known as Lactobacillus bulgaricus, lived longer [1]. Hence was born the concept of probiotics, one that is ever-evolving as evidenced by the surge of publications exceeding several thousand articles. “Pro-biotics” mean “for life” and are defined as live microorganisms, which when consumed in adequate amounts, confer a health effect on the host. In vitro studies suggest that probiotics provide benefit by acting through several different mechanisms [2]. They have an antimicrobial effect through secreting antibacterial substances, compete with pathogens to prevent their adhesion to the intestinal epithelium, compete for Central Michail et al. (2015) Email: Ann Pediatr Child Health 3(2): 1042 (2015) 2/9 nutrients necessary for pathogen survival, produce an antitoxin effect, and reverse some of the consequences of infection on the intestinal epithelium, such as secretory changes and neutrophil migration [3,4]. Probiotics are also capable of modulating the immune system [5], regulating the allergic immune cell response of the body [6] and reducing cell proliferation in cancer [7]. The effects of these agents may go beyond the gastrointestinal tract to distant areas, such as the skin and respiratory mucosa, and it may not be necessary to administer the intact probiotic organism to achieve benefits. At the basic research level, products of probiotics such as secreted proteins and DNA can block inflammation and stop the death of epithelial cells [8,9]. For example, DNA from some probiotic preparations can suppress experimental colitis in several animal models [10]. Probiotic products vary greatly from single agents, double agents, or as combination therapies. Examples of such strains include E-coli, lactobacilli, bifidobacteria, and saccharomyces. Considerable differences exist in the bioavailability, biological activities, doses and composition among probiotic preparations and probiotic studies are frequently characterized by significant heterogeneity. It is also important to recognize that in vitro effects of a probiotic may display opposite behavior in vivo [11]. Therefore, while probiotics are promising agents to unravel the mystery of gut microbial interactions, our understanding of their use for children in the appropriate clinical circumstances is still in its early stages. The purpose of this review is to provide an update on the safety and efficacy of probiotics with a focus on children.