Vitamins are organic molecules that the body can’t synthesize itself, and are necessary for the chemical reactions that maintain life. Vitamins are either water soluble or fat soluble.
In my opinion, the most important vitamins that us western humans should be concerned about are the fat soluble ones, especially D and K. These are the two vitamins that are commonly lacking in western populations and have been shown to have a massive effect on our health. The other vitamins, A, E, the Bs and C should take care of themselves automatically by eating a varied and healthy diet.
Here I’m gonna write a short fat soluble vitamin guide (A, D, E and K), where to get them, how they function and if there’s anything we need to do about all of it.
The storage form of fat soluble Vitamin A in the body is called Retinol. From there, it can be turned into Retinal or Retinoic Acid. Retinal is a crucial component in the retina of the eye, helping to turn the energy of light into an electrical signal that gets sent to the brain, enabling us to see. Retinoic acid is a different form of Vitamin A, it gets transported into the nucleus of cells, regulating gene expression (turning genes on or off), therefore its function is similar to a steroid hormone.
There are several dietary sources of Vitamin A. The one that is best absorbed is Retinol, which we get mostly from animal food, especially liver. Cod fish liver oil contains a lot, eggs contain some and certain high-fat dairy products like butter contain a lot too. The plant forms, the carotenes, are not as bioavailable as the retinol form, but it is possible to get all the Vitamin A you need through vegetables. Carrots, broccoli and sweet potatoes are excellent sources of carotenes.
Unfortunately, deficiency of Vitamin A is very common in children where nutritional status is poor, such as in third world countries. Severe deficiency can cause blindness and death. If you eat a varied, healthy diet with animal food and vegetables, deficiency is very unlikely. Usually the first sign of deficiency is impaired night vision. I don’t recommend that healthy people supplement more than is contained in the average multi, too much can be harmful and cause birth defects.
Fat soluble Vitamin D is produced from cholesterol in the skin when it is exposed to UVB Rays. In the body, the functional form of Vitamin D, calcitriol, functions as a steroid hormone, flowing in to the nucleus of cells and turning genes either on or off. Vitamin D is best known for its role in preventing rickets, a disease that results in softening of bones. In recent times, however, Vitamin D deficiency has been implicated as a key player in all sorts of serious diseases.
The best sources of Vitamin D in the diet are cod fish liver oil, fatty fish and some fortified foods. There is no way to get your daily requirement from food alone, that’s why it’s recommended to try and get regular sun exposure or take a Vitamin D supplement. The D3 form is best since D2 (the plant form) is not nearly as good as maintaining healthy blood levels.
The RDA for Vitamin D is way too low, humans produce more than 15 times that amount in less than a half hour of full-body sun exposure. This is one of the few things I would recommend supplementing with, for anyone who doesn’t get sun throughout the entire year. The Vitamin D Council says to aim for a blood level of 50-80 ng/ml, the only way to know exactly how much to take is to have your doctor to a blood test and adjust your dosage accordingly. Read my detailed Vitamin D guide for more info.
Fat soluble vitamin E is mostly known for its role as a cellular antioxidant, preventing cell membranes from being damaged. It is also considered necessary for proper functioning of the nervous system. There are many different forms of Vitamin E, such as the tocopherols and tocotrienols. The more polyunsaturated fats in your diet, the more of it you need, since they tend to be oxidized easily.
Vitamin E can be obtained through many food sources. Nuts and seeds are excellent sources, along with many types of vegetables such as green leafy vegetables, tomatoes and sweet potatoes. Vitamin E supplementation is definitely not necessary, it is very easy to get all you need from a varied, healthy diet.
The function of fat soluble Vitamin K in the body is altering some specific proteins, enabling them to bind calcium. Vitamin K is intimately involved in blood clotting and is best known for that role, but recent evidence has shown that it is also a key player in bone and cardiovascular health, reducing bone loss and arterial calcification.
There are two dietary forms of Vitamin K: K1 (plant form) and K2 (animal form). The animal form is much better absorbed than the plant form and for optimal health we need to get some of it through diet. The best sources are high-fat dairy like cream, cheese and butter and other animal products such as eggs and meat. The plant form we can get from green leafy vegetables, along with some other kinds of vegetables and fruit.
A deficiency in this fat soluble vitamin is rare, since K2 is also produced by bacteria in the intestine. However, research has shown that our average dietary amounts may not be enough to ensure optimal bone and cardiovascular health. Therefore, it may be a good idea to try and eat more Vitamin K containing foods, or supplementing. For more info check out my detailed Vitamin K guide.
You may be wondering now, where are the RDA numbers? Well, I don’t believe in RDA numbers and I don’t think humans need to be doing any sort of math in order to have a healthy diet. Additionally, the official RDA numbers don’t seem to be in any sort of touch with reality, the Vitamin D RDA of 600IU being a prime example of that.
If you eat a lot of plant foods, consuming some fat along with them greatly improves fat soluble vitamin absorption.