It is well known that deficiencies in certain vitamins and minerals can lead to significant impairment of immune function and an increased susceptibility to infection that can be reversed by supplementation in deficient individuals. “However, it is unclear to what extent supplementation may aid in maintaining an optimal balance within the immune system in adequately nourished individuals.” As I discuss in my video, Kiwifruit for the Common Cold, researchers in New Zealand tried supplementing with whole kiwifruit. In a petri dish, gold kiwifruit puree appeared to boost natural killer cell activity in human blood and also boost the response to the tetanus vaccine. But, does the same thing that happens in a petri dish happen in people? In another study, researchers found that two immune-related sets of genes were upregulated by eating three kiwifruit a day. But, does that translate into actually helping us fight off infection? We didn’t know the answer until recently.
Researchers in New Zealand found that the consumption of gold kiwifruit reduces the severity and duration of certain upper respiratory tract infection symptoms. Why study gold kiwifruits? The study was funded by the company that owns the patent to gold kiwifruits.
In the study, a few dozen elderly individuals were randomized into one or two groups, eating either two bananas a day or four kiwifruit a day for a month, and then switching. The next month, the banana group ate kiwis, and the kiwi group ate bananas. The rationale for providing banana as the “placebo” was to provide an alternative fruit that had relatively similar calories, but lower nutritional value.
The study’s purpose was to determine whether regular consumption of gold kiwifruit reduces the incidence, duration, and severity of symptoms of upper respiratory tract infections, like the common cold, in comparison to bananas. They found no reduction in overall incidence, but those who did get sick during the kiwifruit phase had significantly reduced severity and duration of head congestion, as well as a reduced duration of sore throat. And not just by a little. The sick banana eaters suffered for five days with a sore throat and congestion, compared to the kiwifruit eaters, who felt better after just a day or two. That’s significant.
The reason the researchers studied older individuals is that they tend to be more susceptible to respiratory infections. Small children are another at-risk group, averaging twice as many upper respiratory tract infections as adults, four to six per year. So, in another study, 66 preschoolers were randomized into the same two groups, kiwifruit versus bananas. In the kiwi group, not only were there again significant improvements in the symptoms of those who got sick, fewer got sick in the first place—45% lower odds of a cold or flu-like illness, which means that the children eating kiwis had almost a 50% reduction in the chance of having a cold or flu.
This suggests that kiwifruit consumption may be a “daily prescription for health”; though about 1 in 150 children report being allergic to kiwifruit, which ranks them number three after milk and eggs, and above peanuts, in a survey of 3,500 kids, of the most common food allergies. So, kiwis are not for everybody.
The upside of the financial conflict of interest is that it offers a rare source of funding for fruit and vegetable research. For more on kiwis, see Kiwifruit for Irritable Bowel Syndrome, Kiwifruit and DNA Repair, and Kiwifruit for Insomnia.
What else can we do to lower our risk of pesky respiratory infections? Check out Can Gargling Prevent the Common Cold?, Preventing the Common Cold with Probiotics?, Nutritional Yeast to Prevent the Common Cold, and Using the Produce Aisle to Boost Immune Function.
Michael Greger, M.D.
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