All honey, not just Mānuka has been shown to contain high levels of antioxidants compared to other foods. Antioxidants are important to protect the body from damage caused by free radicals.
Although honey contains high levels of antioxidants, the quantity of honey consumed when only used as a spread makes it quite low compared to other foods. However, if honey is used as an alternative to refined sugar (which contains no antioxidants) the benefit can be quite substantial.
Making those changes can be very easy, replace refined sugar in hot drinks with a teaspoon of honey. If you haven’t tried this already you should, its delicious. It's also a great substitute for refined sugar in baking, and is a great addition to smoothies, cooked meals, desserts, salad dressing, platters, all sorts!
Research about the antioxidant contents of honey was completed by Dr Peter Molan - The antioxidant activity of honey - http://waikato.academia.edu/PeterMolan