In the tenth installment of her "Dangerous or Safe?" series, pediatrician Dr. Cara Natterson sets the record straight on probiotics.

Humans are dependent upon all sorts of tiny organisms to help our bodies function; this co-dependency is probably best illustrated in our intestines, where bacteria ("good bugs") line the walls:

• aiding in the digestion of food
• helping to produce important chemicals such as vitamin K

When your child is sick and takes an antibiotic, the medicine wipes out the bacteria underlying the illness, but also killing many good bacteria in the body at the same time.

Probiotics are essentially the opposite of antibiotics:

• good bugs that can be taken just like medicine
• replenishing the supply of the helpful microorganisms
• aiding various parts of the body like the intestine, bladder, and immune system

Probiotics are not new:

• they have been used for centuries all over the world
• in the U.S., they were approved for over-the-counter sale in 1994
• today, there are more than 300 probiotic supplements on the market, and hundreds more products with probiotics in the ingredient list

The probiotics sold in the U.S. include one or more of the following species of bacteria: Lactobacillus, Bifidobacterium, Enterococcus, Escherichia, and Saccharomyces (the last of which is actually a yeast).

• probiotics are probably really good for us
• many dairy products have "live active cultures," another way of saying probiotics
• the issue with probiotics is simply that it is difficult to know whether you are taking enough to make a difference

What is the bottom line?
Probiotics are safe for most people, but:

• Because probiotics are classified as food supplements, there is little regulation over precisely how much live product makes it into any given powder, tablet, or food, so you may actually wind up under-dosing the probiotic and providing no benefit at all.
• The effectiveness of probiotics also depends upon what you are trying to accomplish: If your child has diarrhea caused by a virus or by antibiotic use, probiotics will likely be helpful, though not if bacteria is the cause.
• Children who have compromised immune systems or have recently undergone bowel surgery should not take probiotics, because they may actually make these children ill.