By Dr. Charlotte Hodges
There is so much information available today about vitamins and supplements, from the internet, to your family doctor, to your best friend’s neighbor’s cousin who had a deficiency. I wanted a chance to read through the data and break down everything that we need to know (and then some) about vitamins and supplements. The series is “Everything you need to know about supplements, from A to Zinc.” While we will review the most common vitamins, I want to also include some lesser known vitamins and supplements as well as the newer supplements that are available.
To start this series, let’s start from the beginning, with Vitamin A. Vitamin A is a fat-soluble vitamin that is most commonly known for its important role in eye health. However, there is much more to this vitamin than meets the eye! There are actually two forms of vitamin A available in the human diet: preformed vitamin A and provitamin A. Preformed Vitamin A is found in foods from animal sources, including dairy products, fish, and meat (especially liver). By far the most important provitamin A carotenoid is beta-carotene, a plant pigment (such as in carrots). Both provitamin A and preformed vitamin A must be metabolized inside the cell to the active forms of vitamin A to support the vitamin’s important biological functions (1-5). The majority of our Vitamin A is stored in our liver.
So what does Vitamin A do?
Vitamin A is involved primarily in eye health. The previtamin and provitamin are metabolized into retinols / retinol esters and stored in the retina of the eye. The retina, located in the back of the eye, has specialized cells that are responsible for color vision and low-light vision. When light hits the back of the eye, a metabolic cascade of events occurs to activate the stored Vitamin A. This allows our brain to interpret the signals as sight and color. However, those with a Vitamin A deficiency can suffer from night blindness, corneal ulcers, and ultimately blindness (7).
As important as Vitamin A is to our visual health, this vitamin also has anti-inflammatory properties and has been found to play a role in immunity, regulation of gene expression and cancer, red blood cell production, and nutrient interactions (7). However, there is some conflicting results on its role in cancer. Therefore, more research is needed in this area.
What happens when you are Vitamin A deficient?
Vitamin A deficiency is the leading cause of PREVENTABLE blindness in low and middle income nations. There is an estimated 19.1 million pregnant women worldwide (especially in Sub-Saharan Africa, Southeast Asia, and Central America) with vitamin A deficiency, and over half of them are affected by night blindness (8). The prevalence of vitamin A deficiency and night blindness is especially high during the third trimester of pregnancy due to accelerated fetal growth. This risk is extended to their children. Half of the children affected by severe vitamin A deficiency-induced blinding xerophthalmia (dry eye from low Vitamin A) are estimated to die within a year of becoming blind (8). The World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) promote vitamin A supplementation as a public health intervention to reduce child mortality in areas and populations where vitamin A deficiency is prevalent (9-11).
Vitamin A also interacts with iron. So patients with low iron (or who are anemic) are at a greater risk for complications from Vitamin A deficiency. Additionally, low Vitamin A can substantially increase the severity and mortality risk of infections, particularly measles and diarrhea (7).
Who is at risk for Vitamin A deficiency?
Since Vitamin A is a fat soluble vitamin, people at the highest risk are those who have altered absorption in their gut, such as post-weight loss surgery patients, those with Crohn’s disease, or those with cystic fibrosis. Premature infants are also at risk for deficiency.
Too much of a good thing?
Patients can intake too much Vitamin A. This was the case of Artic explorers who ate polar bear liver and then suffered the consequences of hypervitamintosis. Excess Vitamin A can lead to increased intracranial pressure (pseudotumor cerebri), dizziness, nausea, headaches, skin irritation, pain in joints and bones, coma, and even death (2,4,5). Pregnant women can also be at risk for birth defects if they include too much of Vitamin A as well.
Bottom Line: Daily requirements
The Recommended Daily Allowance (RDA) is 900 mcg for men and 700 mcg for women. These recommendations increase somewhat for patients who have undergone weight loss surgery.
According to ASMBS, the requirements for patients post-weight loss surgery (WLS) are:
• Sleeve and Gastric Bypass: 5,000 – 10,000 IU daily
• Duodenal Switch: 10,000 IU daily
However, in post-WLS patients with a documented Vitamin A deficiency, their daily requirements will increase. The recommended dosages are based on the presence (or lack of) symptoms.
• Post-WLS patients with deficiency without corneal changes: 10,000-25,000 IU until clinical improvement. (Typically, 1-2 weeks)
• Post-WLS patients with deficiency with corneal changes: 50,000-100,000 IU should be administered intramuscular injection for three days. This is then followed by 50,000 IU / day intramuscular injection for two weeks.
Also, post-WLS patients with a Vitamin A deficiency should also be evaluated for iron and/or copper. Deficiencies in these can impair resolution of a Vitamin A deficiency (6).
REFERENCES
1. Johnson EJ, Russell RM. Beta-Carotene. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:115-20.
2. Ross CA. Vitamin A. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:778-91.
3. Ross A. Vitamin A and Carotenoids. In: Shils M, Shike M, Ross A, Caballero B, Cousins R, eds. Modern Nutrition in Health and Disease. 10th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006:351-75.
4. Solomons NW. Vitamin A. In: Bowman B, Russell R, eds. Present Knowledge in Nutrition. 9th ed. Washington, DC: International Life Sciences Institute; 2006:157-83.
5. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc . Washington, DC: National Academy Press; 2001.
6. J. Parrott et al. 2017. Surgery for Obesity and Related Diseases.
7. Oregon State University, Linus Pauling Institute, Micronutrient Information Center
8. Sherwin JC, Reacher MH, Dean WH, Ngondi J. Epidemiology of vitamin A deficiency and xerophthalmia in at-risk populations. Trans R Soc Trop Med Hyg. 2012;106(4):205-214. (PubMed)
9. World Health Organization. Guideline – Vitamin A supplementation for infants and children 6-59 months of age – Guideline. Geneva 2011.
10. World Health Organization. Guideline – Neonatal vitamin A supplementation Geneva 2011.
11. World Health Organization. Guideline – Vitamin A supplementation for infants 1–5 months of age – Guideline. Geneva 2011.
