A few things to keep in mind are to consume iron rich plant based foods with foods which contains high levels of Vitamin C and cook with a cast iron skillet to maximize absorption. (vespapower.com)
They also generally contain high levels of vitamin C to improve immune function. (ourpaleolife.com)
There is some evidence suggesting that people with higher levels of vitamin D may have a reduced risk of catching the common cold. (verywellhealth.com)