One tablespoon of mayonnaise contains around 6.2 mcg of Vitamin K which only makes up about 5% of the daily recommended amount of Vitamin K for adults. You will want to keep in mind that some of the low or non-fat varieties of mayonnaise contain even less Vitamin K, so you might want to stick with the regular kind if you are going for the most Vitamin K intake.
This vitamin is very important to the body when it comes to doing various things like strengthening bones as well as increasing bone mineral density which is especially important for children and elderly people. Sometimes doctors even give high doses of Vitamin K to newborns in order to prevent brain hemorrhages right after birth. There are certainly a number of benefits to getting enough vitamin K in your diet, though there may be many other healthier ways of getting it than eating mayonnaise.