Babies delivered via caesarean section appear to be at increased risk for various allergic diseases. The thought is that vaginal delivery leads to the first colonization of the baby’s gut with maternal vaginal bacteria. C-section babies are deprived of this natural exposure and have been found to exhibit a different gut flora. This concept is supported by research noting that a disturbance in maternal vaginal flora during pregnancy may be associated with early asthma in their children. This all suggests our natural gut flora can affect the development of our immune system (for better or for worse).
In adulthood, two studies published back in 2001 suggested that probiotics could have systemic immunity-enhancing effects. Subjects given a probiotic regimen saw a significant boost in the ability of their white blood cells to chomp down on potential invaders. (You can watch a video of white blood cells doing their thing in my video Clinical Studies on Acai Berries. A must-see for biology geeks :). And even after the probiotics were stopped, there was still enhanced immune function a few weeks later compared to baseline (check out my 4-min video Preventing the Common Cold with Probiotics? to see the graph). A similar boost was found in the ability of their natural killer cells to kill cancer cells.
Improving immune cell function in a petri dish is nice, but does this actually translate into people having fewer infections? For that, we had to wait another 10 years, but now we have randomized double-blind placebo controlled studies showing that those taking probiotics may have significantly fewer colds, fewer sick days, and fewer symptoms. The latest review of the best studies to date found that probiotics, such as those in yogurt, soy yogurt, or supplements, may indeed reduce one’s risk of upper respiratory tract infection, but the totality of evidence is still considered weak, so it’s probably too early to make a blanket recommendation.
Unless one has suffered a major disruption of gut flora by antibiotics or an intestinal infection—in other words unless one is symptomatic with diarrhea or bloating—I would suggest focusing on feeding the good bacteria we already have, by eating so-called prebiotics, such as fiber. After all, as I noted in Preventing and Treating Diarrhea with Probiotics, who knows what you’re getting when you buy probiotics. They may not even be alive by the time we buy them. Then they have to survive the journey down to the large intestine (Should Probiotics Be Taken Before, During, or After Meals?). Altogether, this suggests that the advantages of prebiotics—found in plant foods—outweigh those of probiotics. And by eating raw fruits and vegetables we may be getting both! Fruits and vegetables are covered with millions of lactic acid bacteria, some of which are the same type used as probiotics. So when studies show eating more fruits and vegetables boosts immunity, prebiotics and probiotics may be playing a role.
How else might we reduce our risk of getting an upper respiratory infection? See:
- Can Gargling Prevent the Common Cold?
- Are Cats or Dogs More Protective For Children’s Health?
- Sleep & Immunity
- The Risks and Benefits of Neti Pot Nasal Irrigation
The immune boosting fruit and vegetable video I reference in Preventing the Common Cold with Probiotics? is Boosting Immunity Through Diet. See also Kale and the Immune System and the subject of my post last week, Boosting Immunity While Reducing Inflammation.
-Michael Greger, M.D.
PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.