Question

One symptom of vitamin A deficiency is impaired night vision.

a) Completely describe the cycle that is important for vision, making sure to indicate where vitamin A plays a role and How would vitamin A deficiency alter this cycle to impair night vision?

Answer 1

Vitamin A deficiency

# introduction

Vitamin A deficiency is most common in Africa and Southeast Asia. It can also occur when the gut can't absorb the nutrient.

Vitamin A is a fat-soluble vitamin that is important for many bodily functions, including proper vision, a strong immune system, reproduction and good skin health.

There are two types of vitamin A found in foods: preformed vitamin A and provitamin .

Preformed vitamin A is also known as retinol and commonly found in meat, fish, eggs and dairy products.

On the other hand, the body converts carotenoids in plant foods, such as red, green, yellow and orange fruits and vegetables, into vitamin A.

# symptoms of vitamin A deficiency

1. Dry skin

Vitamin A is important for the creation and repair of skin cells. It also helps fight inflammation due to certain skin issues (3Trusted Source).

Not getting enough vitamin A may be to blame for the development of eczema and other skin problems.

2. Dry Eyes

Eye problems are some of the most well-known issues related to vitamin A deficiency.

In extreme cases, not getting enough vitamin A can lead to complete blindness or dying corneas, which are characterized by marks called Bitot’s spots

3.Night Blindness

Severe vitamin A deficiency can lead to night blindness (11Trusted Source).

Several observational studies have reported a high prevalence of night blindness in developing nations (12Trusted Source, 13Trusted Source, 14Trusted Source, 15Trusted Source).

Due to the extent of this problem, health professionals have worked to improve vitamin A levels in people at risk of night blindness.

In one study, women with night blindness were given vitamin A in the form of food or supplements. Both forms of vitamin A improved the condition. The women’s ability to adapt to darkness increased by over 50% over six weeks of treatment

4. Infertility and Trouble Conceiving

Vitamin A is necessary for reproduction in both men and women, as well as proper development in babies.

If you are having trouble getting pregnant, a lack of vitamin A may be one of the reasons why. Vitamin A deficiency can lead to infertility in both men and women.

5.Delayed Growth

Children who do not get enough vitamin A may experience stunted growth. This is because vitamin A is necessary for the proper development of the human body.

Several studies have shown that vitamin A supplements, alone or with other nutrients, can improve growth. Most of these studies were conducted in children in developing nations

6.Throat and Chest Infections

Frequent infections, especially in the throat or chest, may be a sign of vitamin A deficiency.

Vitamin A supplements may help with respiratory tract infections, but research results are mixed.

7.Poor Wound Healing

Wounds that do not heal well after injury or surgery may be linked to low vitamin A levels.

This is because vitamin A promotes the creation of collagen, an important component of healthy skin. Research suggests that both oral and topical vitamin A can strengthen skin.

8.Acne and Breakouts

Since vitamin A promotes skin development and fights inflammation, it may help prevent or treat acne.

Multiple studies have linked low vitamin A levels to the presence of acne

A)

Why is vitamin A needed for night vision to occur?

Vitamin A (all-trans-retinol) is a precursor to the formation of the photopigment rhodopsin, which is located in the rods. In order for rhodopsin to be formed, vitamin A must be converted to 11-cis-retinal. This can occur in one of two ways. Vitamin A (all-trans-retinol) can be converted to 11-cis-retinol by isomerase. This 11-cis-retinol can then be converted to 11-cis-retinal. Alternatively, vitamin A (all-trans-retinol) can be converted to all-trans-retinal which can then be converted to 11-cis-retinal. Now that 11-cis-retinal has been formed by either method, it can combine with scotopsin to form the rhodopsin. As rhodopsin absorbs light in the rods, a conformational change occurs in 11-cis-retinal to become all-trans-retinal. A conformational change also occurs in the opsin fragment to form metarhodopsin II, which is the activated form of rhodopsin. The metarhodopsin II then stimulates transducin, a G-coupled protein found on the surface of the disk within the outer membrane in the rod cell. This activation of transducin causes an activation in cGMP phosphodiesterase, which will remove the cGMP mediated activation of cGMP-gated channels that are letting Na+ ions leak into the rod cytoplasm resulting in a hyperpolarization of that rod cell. Thus, in the presence of light, the blockage of Na+ movement into the rod cell will result in a hyperpolarization of that rod cell which then allows messages about light being seen during night vision to be sent to the brain for final interpretation.

In addition to vitamin A's role in helping the rods in our eyes convert light into neuronal impulses for our brain, it is also required to maintain normal differentiation of the cornea and conjunctival membranes which helps prevent other abnormal eye conditions, such as xerophthalmia.

# Summary:

Vitamin A, is a well known fat soluble vitamin found in many supplements and foods.As it relates to eyesight, vitamin A (also called all-trans-retinol) has been shown to be useful in helping with night vision.Vitamin A is a precursor of rhodopsin, the photopigment found in rods within the retina of our eye that helps us to see at night. Without vitamin A, "night blindness" occurs.As with any medication or supplement, excessive doses or unnecessary exposure can be harmful. Therefore, doses above the UL should be avoided because Vitamin A has been associated with an increase risk for hip fracture in postmenopausal women, lung cancer, cardiovascular mortality and total mortality.