維他命A的益處，食物來源，缺乏症和劑量

Vitamin AVitamin A is a major fat-soluble vitamin in the body, rich in antioxidants, and helps improve resistance to certain diseases. It also helps maintain the normal function of the eyes, hair, teeth, gums, and mucous membranes. Vitamin A is involved in fat metabolism and the production of white blood cells. Some studies suggest that vitamin A may prevent DNA or blood vessel damage.

Vitamin A form

Vitamin A is a fat-soluble vitamin that exists in two forms: retinol, found in animal tissues, and beta-carotene, found in plants. (Beta-carotene is sometimes called provitamin A because the body needs to break it down into vitamin A to exert its vitamin function.)

Food sources of Vitamin A

Whole milk, butter, offal, carrots, sweet potatoes, kale, squash, spinach, arugula, red bell peppers, dark green vegetables, liver, cheese, cod liver oil, egg yolks, and almonds.

Symptoms of Vitamin A Deficiency

Night blindness
Childhood developmental delay
Dry skin, dry eyes
Weakened immunity

Food Sources, Benefits and Dosage of Vitamin K

Health benefits of vitamin A

1. Protect your eyes against aging and night blindness

Vitamin A produces pigment in the retina of the eye; therefore, a decrease in vitamin A levels can cause retinal discomfort. On the other hand, high vitamin A levels can protect the eyes from night blindness, meaning the eyes can see even in low light. For older adults, taking sufficient vitamin A can slow down eye aging.

2. Boost immunity

White blood cells help the body mount an immune response against diseases and tumors. Fortunately, vitamin A helps keep white blood cells intact, which can capture and remove bacteria and other antigens produced in the bloodstream. Vitamin A acts as an antioxidant in the body and helps prevent cell and DNA damage.

3. Maintain bone health

A developing body needs vitamin A to maintain bone growth and development, and research has linked vitamin A deficiency with poor bone development. Children with low vitamin A levels have a higher risk of bone fractures than children with normal levels.

Vitamin A dosage

The table below shows the recommended daily dose of Vitamin A for people at different stages of life:

Age (years)	child	a male	female	pregnancy	Breastfeeding
1-3	1,000 IU
4-8	1,320 IU
9-13	2,000 IU
14-18		3,000 IU	2,500 IU	2,310 IU	4,000 IU
19+		3,000 IU	2,500 IU	2,310 IU	4,300 IU

Possible side effects of Vitamin A

Please note that our bodies cannot eliminate excess vitamin A, so taking too much vitamin A can have adverse effects. For example, studies have shown that taking 25,000 IU of vitamin A can cause acute vitamin A poisoning. This person may experience a variety of symptoms, including poor appetite, nausea, vomiting, abdominal pain, or other symptoms such as headache, brittle bones, muscle pain, weakness, or blurred vision.

Meanwhile, for women who are pregnant or may become pregnant, the daily intake of vitamin A should be limited to less than 10,000 IU, as excessive intake of vitamin A may cause birth defects. Additionally, pregnant women and patients with liver problems or hypothyroidism should not tolerate large amounts of vitamin A.

Taking Vitamin A supplements

Vitamin A is available in softgels, tablets, and drops. Vitamin A in the beta-carotene form is available in softgels and tablets. Vitamin A drops can be taken directly into the mouth or mixed with fruit juice or food. Many cereals, juices, dairy products, and other processed foods are fortified with vitamin A. Additionally, please note that taking vitamin A-derived prescription medications (such as isotretinoin and etretinate) with vitamin A supplements may cause toxicity.