The vitamin content can considerably vary depending on climate and soil conditions, variety, fertilization, maturity, harvesting methods, transport and storage.

The preparation of food also has a significant influence. Many vitamins are sensitive to heat, light and oxygen, and watering fruits and vegetables can lower vitamin levels. Gentle processing helps to keep vitamin loss as low as possible: avoid soaking fruits and vegetables before chopping, scrubbing, and washing them. Eat raw fruits and vegetables if possible. Cook vegetables in little water or use a food steamer. Do not put vegetables into the water before it boils. Where possible, the water used for cooking vegetable can be re-used for soups or sauces as many vitamins are retained in it.