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Vitamins

Vitamin A and Beta-Carotene Facts

Why you need Vitamin A

  • Vitamin A promotes vision
  • Participates in protein synthesis and cell differentiation and thus maintains the health of skin.
  • Supports reproduction and growth
  • Immune function
  • Bone metabolism

Vitamin A helps maintain a clear outer window, the cornea and helps in the conversion of light energy into nerve impulses at the retina.  Only one-thousandth of the body's vitamin A is in the eye. Much more is used in lining of cells on the body. Vitamin A helps to protect your skin from the harmful effects of too much sun exposure.

Retin-A a relative of Vitamin applied topically on the skin can prevent acne, wrinkles, and other skin disorders.

Vitamin A Deficiency

90 percent of Vitamin A stores in your liver. If you stopped eating any Vitamin A enriched foods it could take one to two years to deplete your Vitamin A storage for an adult, but sooner for a growing child.

However even with the body's ability to store up Vitamin A there are countries in the world where children live in a Vitamin A deficient state causing them to be vulnerable to diseases and blindness. Night blindness is the first indication of a person being deficient in Vitamin A.

Too Much Vitamin A

Children are most sensitive to overdose of Vitamin A through the use of supplements. Too much Vitamin A can cause bone defects.10,000 IU of supplemental Vitamin A every day before the seventh week of pregnancy can cause the most damage.

Other possible symptoms of too much Vitamin A include: nausea, jaundice, irritability, anorexia (not to be confused with anorexia nervosa, the eating disorder), vomiting, blurry vision, headaches, hairloss, muscle and abdominal pain and weakness, drowsiness, and altered mental status.

In general, acute toxicity occurs at doses of 25,000 IU/kg of body weight, with chronic toxicity occurring at 4,000 IU/kg of body weight daily for 615 months. However, liver toxicities can occur at levels as low as 15,000 IU per day to 1.4 million IU per day, with an average daily toxic dose of 120,000 IU per day. In people with renal failure, 4000 IU can cause substantial damage. In addition, excessive alcohol intake can increase toxicity. Children can reach toxic levels at 1,500 IU/kg of body weight.

High vitamin A intake has been associated with spontaneous bone fractures in animals. Cell culture studies have linked increased bone resorption and decreased bone formation with high vitamin A intakes. This interaction may occur because vitamins A and D may compete for the same receptor and then interact with parathyroid hormone, which regulates calcium.

Vitamin A Recommended Daily Intake

Life Stage Group Recommended Dietary Allowances (RDA)
 

Adequate Intakes (AI*)
μg/day

Upper Limit
 

μg/day

Infants

06 months
712 months


400*
500*

600
600
Children

13 years
48 years


300
400

600
900
Males

913 years
1418 years
19 - >70 years


600
900
900

1700
2800
3000
Females

913 years
1418 years
19 - >70 years


600
700
700

1700
2800
3000
Pregnancy

<19 years
19 - >50 years


750
770

2800
3000
Lactation

<19 years
19 - >50 years


1200
1300

2800
3000

Note that the limit refers to synthetic and natural retinoid forms of vitamin A.

Vitamin A is found naturally in many foods:


* liver (beef, pork, chicken, turkey, fish) (6500 μg 722%), including cod liver oil
* carrot (835 μg 93%)
* broccoli leaf (800 μg 89%) - According to USDA database broccoli florets have much less.[10]
* sweet potato (709 μg 79%)
* butter (684 μg 76%)
* kale (681 μg 76%)
* spinach (469 μg 52%)
* pumpkin (400 μg 41%)
* collard greens (333 μg 37%)
* Cheddar cheese (265 μg 29%)
* cantaloupe melon (169 μg 19%)
* egg (140 μg 16%)
* apricot (96 μg 11%)
* papaya (55 μg 6%)
* mango (38 μg 4%)
* pea (38 μg 4%)
* broccoli (31 μg 3%)
* milk (28 μg 3%)

Note: data taken from USDA database bracketed values are retinol activity equivalences (RAEs) and percentage of the adult male RDA, per 100 grams of the foodstuff (average).

Conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies. Getting Vitamin A in natural food is much more easily used by the body than A in supplement form. It would be difficult to get too much A by eating food alone as compared to supplements. I take supplements for certain things like Omega-3s,  but no longer take multi-vitamins as I believe most general vitamins like A can be readily acquired by simply eating fruits and vegetables. Omega 3 however, you have to be careful in how much fish you eat as many varieties of fish now contain mercury.


list of sources of Vitamin A

Amaranth Leaves
Apricots
Bok Choy
Broccoli
Brussels Sprouts
Butternut Squash
Cantaloupe
Carrots
Chestnuts
Chinese Broccoli
Chinese Cabbage
Eggs
Kale
Leeks
Mangos
Milk
Papayas
Peaches
Peas
Pecans
Pistachios
Pumpkin
Rapini
Spinach
Squash - summer
Squash - winter
Sweet Potato
Swiss Chard

 

Sources: 
Understanding Nutrition

http://www.vitamina.org/

Books on Vitamins for further research.


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