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, which 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. So, researchers in New Zealand tried supplementing with kiwifruit. In a petri dish, gold kiwifruit puree appeared to boost natural killer cell activity in human blood and boost the response to the tetanus vaccine, but does what happens in petri dishes happen in people?

There was a study in which two immune-related sets of genes were found to be upregulated by eating three kiwifruit a day. But, do they actually help us fight off infection? We didn’t know, 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 kiwi fruits? Because the study was funded by the company that owns the patent to gold kiwi fruits. A few dozen elderly individuals were randomized into one of two groups, eating two bananas a day, or eating four kiwifruit a day for a month, and then they switched. 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 purpose of the study 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 that did get sick during the kiwifruit phase had significantly reduced severity and duration of head congestion, and the 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 they 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, 66 preschoolers were randomized into the same two groups, kiwifruit versus bananas, and not only were there again significant improvements in the symptoms of those that got sick on kiwifruit, 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; however, about 1 in 150 children report being allergic to kiwifruit, which ranks them #3 after milk and eggs, and above peanuts, in a survey of 3,500 kids, as the most common food allergies. And so, they are not for everybody.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

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