MUSC News Center
Foods that fight the flu
Debbie Petitpain | MUSC News Center | October 14, 2014
It’s that time of year again. The nights are cooler, the days are shorter, the mornings are crisp. It’s fall. And with it, comes cold and flu season. As people spend more time inside and in close quarters with others, it becomes easier to spread germs and disease. While there are no scientifically proven direct links between lifestyle and enhanced immune function, it is easy to fortify your defenses with some healthy food choices.
The gut is populated with a complex of microorganisms referred to as the gut flora or microbiota. These “bugs” protect against pathogens through a variety of possible mechanisms, including inhibition of the growth of pathogens by competing for nutrition, limiting movement across the intestinal wall by competing for sites of absorption, and by producing antimicrobial metabolites and possibly acidifying the environment so “bad bugs” can’t thrive.
Your diet feeds you AND your gut microbiota and can be used to increase the ratio of the “good-for-you” bugs, referred to as probiotics, in the gastrointestinal tract. Fermented foods are tried and true sources of probiotics (just watch out for the added sugars in yogurt and kefir and the sodium content in sauerkraut and kimchi). Friendly bacteria also feed off of soluble fiber from foods like oatmeal, lentils, apples, nuts, flaxseeds, and beans. While many claim they benefit from taking probiotics in supplement form, the U.S. Food and Drug Administration (FDA) has approved no specific health claims for probiotics in a pill.
Sundried, shiitake mushrooms, fatty fish, fortified dairy productions and other fortified foods are good sources of vitamin D. Vitamin D, which is actually a hormone, has been well studied for its role in mineral metabolism and skeletal health. Emerging science has found vitamin D receptors and the vitamin D activating enzyme in all types of cells throughout the body including intestine, pancreas, prostate and cells of the immune system. This has spurred further research into the role of vitamin D beyond building strong bones.
Vitamin D may stimulant the innate immune system through several mechanisms. Calcitriol, the biologically active form of vitamin D that circulates in the blood, enhances the antimicrobial effects of the immune system cells that fight against pathogens and activates production of antimicrobial proteins. Vitamin D many also indirectly play a role in the initiation of the adaptive immune response by altering the function and structure of certain monocytes, a type of white blood cell.
The body does make endogenous vitamin D when exposed to the sun, however, adequate sun exposure fluctuates throughout the year and few people get enough UV exposure during cold and flu season. With few food sources of vitamin D, many people benefit from vitamin D supplementation. The Institute of Medicine has set the recommended daily allowance for adults at 600 IU, although many clinicians recommend more (IOM sets the upper safety limit at 4000 IU).
Allicin may enhance the immune response by significantly stimulating the proliferation of lymphocytes. Limited intervention studies shows prophylactic treatment with garlic decreases the number of self-reported colds. While allicin is the most studied, related organosulfur compounds have been found in other allium foods as well as broccoli, cabbage, radish, asparagus and even coffee, many of which may be more palatable to take on a daily basis (unless you are also trying to ward off vampires).