Its counterpart in blueberries is a compound called pterostilbene.
The new findings are published in the journal Molecular Nutrition and Food Research.
Scientists screened 446 compounds for their immune system activity.
"Out of a study of hundreds of compounds, just these two popped right out," said lead researcher Dr Adrian Gombart, from Oregon State University in the US.
"Their synergy with vitamin D.. was significant and intriguing. It's a pretty interesting interaction."
Story continues below the slideshow:
Top Foods For Your Immune System
Good Old Chicken Noodle Soup (01 of11)
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Grandma was right -- nothing beats chicken soup for fending off sniffles. Not only does it provide the fluids needed to help fight off viruses, it's a powerful mucus stimulant so it helps clear nasal congestion as well as thin mucus. It's also thought to have a mild anti-inflammatory effect than can help ease cold symptoms. Keep some organic chicken stock on hand, because studies have found that even commercial soup is as effective as homemade. (credit:Shutterstock)
Healers With Flavour (02 of11)
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If you want to punch up the healing power of your chicken soup - or any other dish -- add plenty of garlic and onions. When combined, these flavorful healers contain numerous antiseptic and immunity boosting compounds. As an added plus, garlic helps to open clogged sinuses. (credit:Shutterstock)
Shroom It Away (03 of11)
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No herbal medicine cabinet should be without mushrooms. They increase the production of cytokines, which are cells that help fight off infection. They also contain polysaccharides, which are compounds that support the immune system. The most potent cold- and flu-fighting 'shrooms are shitake, maitake and reishi. (credit:Shutterstock)
Keep The Citrus (04 of11)
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Citrus fruits contain hefty doses of powerhouse vitamin C. Studies have found that this antioxidant can reduce cold symptoms by 23 percent, and all that's needed is just one to eight grams (1,000 to 8,000 milligrams) to do the trick. Besides citrus fruits, other foods that have high amounts of vitamin C include papaya, sweet potatoes, butternut squash, tomatoes, broccoli, brussel sprouts and red bell peppers. (credit:Shutterstock)
Why Yogurt Works (05 of11)
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Studies have shown that eating a cup of low-fat yogurt each day can reduce your susceptibility to colds by 25 per cent. The beneficial bacteria is Lactobacillus reuteri which has been found to block the replication of viruses that invade the body when we get sick. Not all brands have that particular bacteria, so check labels and be sure to go organic. (credit:Shutterstock)
Immune-Boosting Supplements (06 of11)
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While yogurt is a great source of probiotics, some have more than others and we can really benefit by taking an additional supplement. Other immune-booster "musts" are vitamin D and Omega 3 fatty acid. (credit:Shutterstock)
Sipping Tea (07 of11)
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Hot tea is soothing and a great home remedy, helping to thin mucus and ensure proper hydration. For added health benefit, sip green or black tea -- both are filled with flavonoids, which are potent antioxidants. (credit:Shutterstock)
Ginger Aid (08 of11)
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Ginger comes to the aid when we're sick in some powerful ways. Besides soothing a scratchy throat, it has chemicals called sesquiterpenes that target rhinoviruses - which are the most common family of cold viruses - as well as substances that help suppress coughing. Ginger is also a natural pain and fever reducer and a mild sedative so you'll feel more comfortable and be able to rest easier. Add a couple of tablespoons of shredded gingerroot to your tea, or make ginger tea (it comes in tea bags, but you can also simmer fresh sliced ginger to make a potent brew). (credit:Shutterstock)
Honey, My Immune System Rocks (09 of11)
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Honey has numerous medicinal properties and because it coats your throat it is a natural way to soothe sore throats. It also has antioxidant and antimicrobial properties to help fight infections from viruses, bacteria, and fungi. Skip the common clover honey that you'll find in the supermarket as it has the lowest antioxidant level. Look for buckwheat honey, which has the highest. (A note of caution: never give honey to children under one years of age because their immune systems are not developed enough to ward off infantile botulism, which is carried in honey spores.)
Get Peppy (10 of11)
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It's ironic that black pepper -- the spice best known for making you sneeze -- can ward off the sniffles. Black peppercorns are high in piperine, a compound known for its anti-fever and pain-relieving qualities. (credit:Shutterstock)
Make It Spicy (11 of11)
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Make recipes more flavorful with garlic, thyme, rosemary, sage and oregano -- while spicing things up, you'll also get an added kick of immune-busters, too. (credit:Shutterstock)
With the help of vitamin D, the compounds significantly boosted activity of the cathelicidin antimicrobial peptide (CAMP) gene.
CAMP has been shown to play a key role in the "innate" immune system, which is the body's first line of defence against infection.
The innate immune response is especially important for fending off bacteria, which are increasingly becoming resistant to antibiotics.
A strong link has been established between adequate vitamin D levels and CAMP gene function.