Vitamin A, also called retinol, and vitamin K are essential nutrients belonging to the fat-soluble group of vitamins. Along with vitamins D and E, the other two fat-soluble vitamins, they stay in your fat tissue and liver after you consume them. In contrast, your body expels water-soluble nutrients in urine. Although both vitamins share some traits, such as solubility, they have different roles in the functioning of your body.
Types
Retinol occurs naturally, and manufacturers can create synthetic versions. Your body also produces retinol after you eat fat-soluble substances known as carotenoids, such as beta-carotene. Natural retinol and retinol derived from carotenoids are both antioxidants. The natural and synthetic forms are toxic in large quantities, as well, while retinol made from carotenoids is generally nontoxic. Similar to retinol, vitamin K has three basic variants. The manmade form called vitamin K-3, or menadione, is twice as powerful as the natural form named vitamin K-1, or phylloquinone. Live bacteria in the gastrointestinal tract make the third type, referred to as vitamin K-2 or menaquinone.
Functions
Besides playing a role in your genes and reproductive system, retinol helps retain moisture in your eyes, skin and the lining of your lungs, mouth, nose and throat. The vitamin also helps your eyes refocus in different types of light, and it contributes to the proper development of your bones and teeth. Other functions of retinol include helping cells divide correctly, preventing cataracts and treating various health conditions, such as premenstrual syndrome in women, low sperm count in men, acne, gastrointestinal ulcers and gum disease. Vitamin K allows your blood to clot normally and, according to the National Institutes of Health, may also help bones remain healthy in elderly people.
Food Sources
The natural form of retinol comes from certain animal food sources, including fish, cod liver oil, liver and dairy products. Yet retinol derived from carotenoids such as beta-carotene comes from plant sources, including fruits such as apricots and cantaloupe and vegetables such as carrots, spinach and sweet potatoes. Vitamin K comes from assorted animal and plant foods, too. Common animal sources of the nutrient include eggs, fish and liver. Typical plant foods with substantial vitamin K include green and leafy vegetables, such as broccoli, Brussels sprouts, collards, kale and turnips. Cheddar cheese and green tea contain a large amount of vitamin K, as well.
Recommended Intake
Health-care specialists measure retinol in portions called international units, or IUs, and vitamin K in units called micrograms, or mcg. Babies younger than 1 year old need approximately 1,875 IU of retinol and 10 mcg of vitamin K per day. Children ages 1 to 10 need about 2,000 to 3,500 IU of retinol and 15 to 30 mcg of vitamin K daily. All other individuals should consume roughly 4,000 to 6,500 IU of retinol and 45 to 80 mcg of vitamin K each day.
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