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#immunity

Vitamin A: Moderation Is Key

Person wearing black holding an apple in their hand

We are what we eat, but for most of us the nutrients and vitamins we take in daily are poorly understood and frequently taken for granted. So in an effort to gain appreciation for these important nutrients, I have decided to study and write about a few in particular starting with Vitamin A.

What is vitamin A?
The term “vitamin” refers to any nutrient required by a living organism that can’t be self synthesized and must be obtained from your diet. In the case of Vitamin A, the name actually refers to several different compounds that have similar biochemical functions. These compounds include Retinol, Retinal, and four carotenoids including beta carotene. Vitamin A is most commonly known for its role in vision, but also plays an important role in gene transcription, immune function, bone growth, reproduction, Iron transport, and blood cell formation.

What are the recommended daily allowances and upper levels of intake?

Adult RDA or RDI for Vitamin A
Males(18+): 900 mcg/day RAE (3000 International Units)
Females (18+): 700 mcg/d RAE (2300 International Units)

 

  • Pregnancy 750-770 mcg/day RAE (2500-2600 International Units)
  • Lactation 1200-1300 mcg/day RAE (4000-4300 International Units)

Upper Limit of intake (UL)

Adults: 3000 mcg/day RAE (10,000 International Units)

Pregnancy: 2800 mcg/day RAE (9200 International Units)
Lactation: 3000 mcg/day RAE (10,000 International Units)

Pediatric RDA

1-3 years old: 300 mcg/day RAE (1000 International Units)
4-8 years old: 400 mcg/day RAE (1333 International Units)
9-13 years old: 600 mcg/day RAE (2000 International Units)
14-18 years old: 900 mcg/day RAE (3000 International Units)

Pediatric Upper Limits of normal intake

0-3 years old: 600/day mcg RAE (2000 International Units)
4-8 years old: 900/day mcg RAE (3000 International Units)
9-13 years old: 1700 mcg/day RAE (5700 International Units)
14-18 years old: 2800 mcg/day RAE (9200 International Units)

What happens when you are Vitamin A deficient?

Those at risk for vitamin A deficiency include vegans, recent immigrants, alcoholics, preschool children living below the poverty line, patients suffering from fat mal-absorption, Inflammatory bowel disease, cystic fibrosis, sprue, pancreatic insufficiency, and persons who have undergone small-bowel bypass surgery.
One of the first signs of Vitamin A deficiency is poor vision,particularly night blindness. There is also increased interest in subclinical vitamin A deficiency where low storage levels of vitamin A lead to an increased risk of respiratory and diarrheal infections, poor bone development, decreased growth rate, and decreased ability to survive serious illness.
According to the National Institute of Health(NIH)“Vitamin A deficiency is common in developing countries but rarely seen in the United States. Approximately 250,000 to 500,000 malnourished children in the developing world become blind each year from a deficiency of vitamin A. In the United States, vitamin A deficiency is most often associated with strict dietary restrictions and excess alcohol intake.”

What happens when you get too much Vitamin A?

Vitamin A can be derived from two different sources, animal or a plant.Animal source Vitamin A is called preformed vitamin A. It is absorbed in the form of retinol. Retinol is one of the most bioavailable forms of vitamin A. Vitamin A that is found in fruits and vegetables is called provitamin-A carotenoid. These can be made into retinol in the body. As a preformed vitamin is fat soluble, it is more difficult for your body to get rid of excess levels. This makes animal source or preformed vitamin A more dangerous in terms of toxicity because storage levels continue to increase over time. Beta-carotene is a safe source of vitamin A because the conversion of beta-carotene to vitamin A is regulated in the body.

The four main negative effects of toxic levels of vitamin A storage (Hypervitaminosis A) are: birth defects, liver abnormalities, reduced bone mineral density, and central nervous system disorders.
Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time. Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and muscular incoordination. Although hypervitaminosis A can occur when large amounts of liver are regularly consumed, most cases result from taking excess amounts of the nutrient in supplements.

Pregnancy Vitamins

During pregnancy Vitamin A plays several important roles including, neural development and development of heart, ears, eyes, limbs, and lungs. Pregnant mothers need to be careful as excess vitamin A is teratogenic, (a term for anything harmful to the normal physiological development of the baby) The UL(upper limit) during pregnancy is 9200 IU, 800IU lower than that recommended for an adult female as excess Vitamin A may cause cardiovascular, craniofacial, thymus, and nervous system malformations. The following is a warning from the national institute of health;“Over the past 15 years, syntheticretinoids have been prescribed for acne, psoriasis, and other skin disorders. Isotretinoin (Roaccutane® or Accutane®) is considered an effective anti-acne therapy. At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne. The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.”

Sources of vitamin A

So after all of this discussion about what vitamin A is and what it does, the next question is what are the vitamin A levels in common foods we eat? The following is a chart provided by the NIH**.

Table 1: Selected animal sources of vitamin A
Food Vitamin A (IU)* %DV**
Liver, beef, cooked, 3 ounces

27,185

545

Liver, chicken, cooked, 3 ounces

12,325

245

Milk, fortified skim, 1 cup

500

10

Cheese, cheddar, 1 ounce

284

6

Milk, whole (3.25% fat), 1 cup

249

5

Egg substitute, ¼ cup

226

5

 

Table 2: Selected plant sources of vitamin A (from beta-carotene)
Food Vitamin A (IU)* %DV**
Carrot juice, canned, ½ cup

22,567

450

Carrots, boiled, ½ cup slices

13,418

270

Spinach, frozen, boiled, ½ cup

11,458

230

Kale, frozen, boiled, ½ cup

9,558

190

Carrots, 1 raw (7½ inches)

8,666

175

Vegetable soup, canned, chunky, ready-to-serve, 1 cup

5,820

115

Cantaloupe, 1 cup cubes

5,411

110

Spinach, raw, 1 cup

2,813

55

Apricots with skin, juice pack, ½ cup

2,063

40

Apricot nectar, canned, ½ cup

1,651

35

Papaya, 1 cup cubes

1,532

30

Mango, 1 cup sliced

1,262

25

Oatmeal, instant, fortified, plain, prepared with water, 1 cup

1,252

25

Peas, frozen, boiled, ½ cup

1,050

20

Tomato juice, canned, 6 ounces

819

15

Peaches, canned, juice pack, ½ cup halves or slices

473

10

Peach, 1 medium

319

6

Pepper, sweet, red, raw, 1 ring (3 inches diameter by ¼ inch thick)

313

6

As you can see one portion of liver on the animal side and carrots on the vegetable provide 400-550% each of the daily value requirement of vitamin A. Many other sources provider lesser amounts but certainly add up to make vitamin A deficiency unlikely in the typical American diet.
In conclusion, vitamin A plays many important roles in the human body but should be respected in terms of toxicity and may have some implications amongst certain populations for deficiency. Pregnant women need to be most careful with intake and beta carotene is a safer form of vitamin A to use during this time. Finally, a well-balanced diet should provide most people with all of the vitamin A they need.
To Your Health,

Dave Rigby MS, PA-C, member ASN
*definitions of medical terms: http://ods.od.nih.gov/factsheets/
** http://www.ars.usda.gov/main/site_main.htm?modecode=12-35-45-00