Micro Nutrients Part 1, Vitamin A
I apologize for the delay in posting, I’ve been researching the next article on vitamin & mineral supplementation, and the project keeps growing in scope, apparently the subject is much more complicated than I originally envisioned. So instead of waiting till I have all the information and writing one massive post, I’m going to break it down into a long series of articles covering all the various aspects.
Throughout this project, data has been taken from a variety of sources, including wikipedia and “The New Encyclopedia of Vitamins, Minerals, & Supplements”. I looked around for an “Authoritative” work on the subject, and couldn’t find one, even among the medical references. Information contained herein will be as accurate and verified as possible, however this isn’t peer reviewed scientific literature, it’s usable real world information, so educated guesses will be made where appropriate.
We’ve already covered the macro nutrients (protein, carbohydrates, fats), so now it’s time to talk about the micro nutrients. Micro Nutrients are those items in diet our diet which are essential to proper function, but have no calories and are generally consumed in small amounts (from a few grams (g) all the way down to mili grams (mg) at 1/1,000 th of a gram, and micro grams (mcg) which are 1/1,000,000 th of a gram). While you might consume 225 g of protein in a day or even more beneficially, eating that much iodine would be fatal, not to mention not very tasty.
Vitamin A was the first to be discovered in 1913, and is essential to prevent night blindness, a deficiency disease that was quite common in ancient times. Liver contains high levels of Vitamin A and has long been known as a folk remedy for vision related ailments.
Animal sources of Vitamin A come in the form of an Alcohol (retinol), an Aldehyde (retinal), or an acid (retinoic acid). Plant sources come from plant pigments known as carotenes (or carotenoids). Here is a list (non-exhaustive) of foods that contain Vitamin A or it’s precursors:
Liver, Cod Liver Oil, Carrots, Squash, Kale, Mangoes, Cantaloupe, Apricots, Sardines, Tomato Sauce, Milk, Butter, Broccoli, Sweet Potatoes, Green Peppers, Eggs, Spinach, Papaya, and Peas
The absorbtion rate of Vitamin A from plant sources is somewhere between 1/2 to 1/24 as efficient as that from animal sources, though it is enhanced somewhat in the presence of fats. Intake values are usually expressed in terms of retinol which is fully absorbed.
The minimum, maximum, and optimum intake values for all micro-nutrients are somewhat debatable as there is often insufficient research, and correct values can vary with age, sex, activity level, genetic factors, and diet. The RDA (recommended daily allowance) generally represents the minimum value to avoid deficiency plus a safety margin. Values for all three are somewhat hard to pin down, and throughout this series merely represent my “best estimate” when comparing all the different sources available. All values are stated in terms of age 20s - 30s male subjects, women’s intake values are generally about 20% lower, mostly due to lower average bodyweight.
For Vitamin A, the intake range is 900 mcg - 3000 mcg, with 1500 mcg considered to be optimum. Doses of over 3000 mcg can cause birth defects in pregnant women, and doses of over 7500 mcg are toxic to just about everyone. Deficiency symptoms include night blindness, dry skin, retarded growth, and increased susceptibility to infection. Overdose effects include headaches, nausea, vomiting, irritability, drowsiness, joint pain, dry skin, and liver damage. As Vitamin A is fat soluble, it’s much harder for the body to excrete excess, so be careful not to overdose. Toxic effects are most prevalent from animal sources, and highly unlikely when consuming the plant (caratenoid) versions. Alcohol consumption can lower vitamin A absorbtion and deficiency is actually fairly common among alcoholics.
Carotenes such as beta-carotene, alpha-carotene, lutein, lycopene, zeaxanthin, and beta cryptoxanthin are vitamin A precursors that can be stored in the liver. (A precursor can be used by the body to synthesize the required compound) These substances are safe even at high doses, though excessive intake can cause hypercarotenemia which can be identified by the yellowing of the skin. This condition is not very dangerous, and can be fixed merely by lowering intake. There is no official recommended intake, though some experts suggest 10 mg - 30 mg daily. In addition to their role as Vitamin A precursors, carotenes act as anti-oxidants, help to protect against heart disease, and boost immune function.
Tags: Diet, Nutrition, Supplements, Vitamins