Nutrition Diet: What are the two deficiency diseases caused by vitamin A?

According to the World Health Organization, vitamin A deficiency is the leading cause of preventable blindness in children worldwide. While the effects are most prevalent in developing countries, a proper nutrition diet is crucial everywhere to prevent this serious condition. Many wonder, what are the two deficiency diseases caused by vitamin A?

Quick Summary

Vitamin A deficiency leads to serious eye-related health issues. The two primary diseases are night blindness, impairing vision in low light, and xerophthalmia, a progressive eye dryness that can cause irreversible blindness.

Key Points

• Night Blindness: An early symptom where vision is poor in low light due to inadequate rhodopsin production, a retinal pigment requiring vitamin A.

• Xerophthalmia: A progressive eye disease characterized by severe dryness of the conjunctiva and cornea, potentially leading to irreversible blindness.

• Immune System Impact: Deficiency weakens the immune system, increasing the risk and severity of infections like measles and diarrhea.

• Dietary Prevention: VAD is best prevented by consuming a balanced diet rich in preformed vitamin A from animal sources and carotenoids from plant sources.

• Treatability: Early stages, like night blindness, can be reversed with vitamin A supplements, but damage from advanced xerophthalmia is permanent.

• Global Health Issue: Though rare in developed nations, VAD remains a major public health problem in developing countries, particularly affecting young children.

• Absorption Issues: Conditions like cystic fibrosis, celiac disease, and chronic liver disease can impair vitamin A absorption, requiring special management.

The Importance of Vitamin A in a Healthy Diet

Vitamin A is a fat-soluble vitamin essential for a multitude of bodily functions, playing a critical role in vision, immune function, cell growth, and reproduction. It is an indispensable component of a healthy nutrition diet, as the human body cannot produce it on its own. A deficit can trigger a spectrum of health issues, ranging from mild skin conditions to severe, sight-threatening diseases. The most significant consequences, however, are related to eye health, manifesting in two primary deficiency diseases: night blindness and xerophthalmia.

The Primary Deficiency Diseases Caused by Vitamin A

Night Blindness (Nyctalopia)

Night blindness is often one of the earliest and most prevalent symptoms of vitamin A deficiency (VAD). This condition affects an individual's ability to see clearly in low-light conditions, such as at dusk or in a dimly lit room, while daytime vision remains relatively normal.

• Mechanism: Vitamin A is a key component of rhodopsin, a pigment found in the rod cells of the retina that is crucial for detecting low light. When the body is deficient in vitamin A, it cannot produce enough rhodopsin, leading to impaired night vision.
• Reversibility: Unlike the more severe forms of VAD, night blindness is often reversible with prompt and adequate vitamin A supplementation.
• Population: It is a common problem among pregnant women and young children in developing countries where VAD is widespread.

Xerophthalmia

Xerophthalmia is a progressive and more severe eye condition that results from a prolonged and serious deficiency of vitamin A. This term encompasses a range of clinical signs, from dryness of the eye's surface to complete corneal destruction and permanent blindness.

• Progression: The disease develops through a series of stages:
  • Conjunctival Xerosis: The conjunctiva, the thin membrane covering the white of the eye, becomes dry, wrinkled, and loses its normal luster.
  • Bitot's Spots: Foamy, triangular patches of keratinized material appear on the conjunctiva.
  • Corneal Xerosis: The cornea, the transparent front part of the eye, becomes dry and dull.
  • Keratomalacia: In this advanced stage, the cornea softens and ulcerates, potentially leading to perforation.
  • Corneal Scarring: The final stage of severe VAD, leading to irreversible blindness.
• Irreversibility: Unlike night blindness, the vision loss from advanced xerophthalmia, especially due to scarring, is permanent and cannot be corrected with supplements.

Beyond the Eyes: Other Health Impacts of VAD

While eye-related diseases are the most prominent, a lack of vitamin A affects other parts of the body as well, particularly for vulnerable populations like young children and pregnant women.

• Impaired Immune Function: Vitamin A is vital for the proper function of the immune system. Deficiency can weaken the body's ability to fight off infections, increasing the severity and risk of infectious diseases like measles, diarrhea, and respiratory illnesses.
• Delayed Growth and Development: In children, VAD can cause slowed growth and bone development, contributing to overall malnutrition.
• Skin Problems: A deficit can lead to dry, scaly, and thick skin, a condition known as follicular hyperkeratosis.
• Infertility and Reproductive Issues: For both men and women, vitamin A plays a role in reproductive health. Deficiency can cause infertility and increase the risk of maternal and fetal death during pregnancy.

Prevention and Treatment through Nutrition

Preventing vitamin A deficiency hinges on maintaining an adequate intake of the vitamin through diet or supplementation. Treatment for diagnosed deficiency involves high-dose supplementation, often administered orally.

Dietary Sources of Vitamin A

To ensure sufficient intake, a balanced diet should include a variety of both preformed vitamin A (retinoids) from animal products and provitamin A carotenoids from plant sources.

• Animal Sources (Retinoids)
  • Liver (the richest source)
  • Eggs
  • Milk and fortified dairy products
  • Oily fish (salmon, tuna)
• Plant Sources (Carotenoids)
  • Carrots
  • Sweet potatoes
  • Dark leafy green vegetables (spinach, kale)
  • Pumpkin and squash
  • Orange and yellow fruits (mangoes, papaya)

Comparison of Vitamin A Sources

Understanding the different forms of vitamin A helps in planning a balanced diet. Animal-based sources provide preformed vitamin A, which is highly bioavailable, while plant-based sources offer carotenoids that the body must convert.

Feature	Animal-based (Retinoids)	Plant-based (Carotenoids)
Form	Preformed vitamin A (e.g., retinol)	Provitamin A (e.g., beta-carotene)
Sources	Liver, eggs, milk, fish	Carrots, sweet potatoes, dark leafy greens, pumpkin, mangoes
Absorption	Highly bioavailable (75-100%)	Variable (approx. 40-60%), depends on food and cooking method
Conversion	Active form; no conversion needed	Converted to vitamin A by the body
Best Absorbed With	Some dietary fat	Some dietary fat and cooking

Other Factors Influencing VAD

Beyond poor dietary intake, certain conditions can interfere with the body's ability to absorb or utilize vitamin A, including:

• Fat malabsorption disorders (e.g., cystic fibrosis, celiac disease)
• Chronic liver disease, which impairs vitamin A storage
• Bariatric or other intestinal surgery

These situations often require specialized medical attention and supplementation, as diet alone may not be sufficient to correct the deficiency.

Conclusion

In summary, the two deficiency diseases caused by vitamin A are night blindness and xerophthalmia, both of which severely impact vision. While night blindness can often be reversed with supplementation, xerophthalmia can lead to permanent blindness if left untreated. Beyond these specific eye conditions, vitamin A deficiency impairs the immune system and hinders growth and reproduction. Fortunately, VAD is preventable and treatable through a balanced nutrition diet rich in vitamin A sources, and via targeted supplementation, especially for at-risk populations. A varied diet that includes both animal and plant sources, alongside addressing any underlying absorption issues, is the most effective approach for ensuring adequate vitamin A levels and protecting overall health. For further information, consider consulting a reliable resource such as the World Health Organization (WHO)(https://www.who.int/data/nutrition/nlis/info/vitamin-a-deficiency).

Frequently Asked Questions

What is the main cause of vitamin A deficiency?

The main cause of vitamin A deficiency is inadequate intake of vitamin A in the diet. This is most common in developing countries where diets may lack sufficient amounts of vitamin A-rich foods, especially animal products and specific fruits and vegetables.

Can night blindness be reversed with treatment?

Yes, night blindness caused by vitamin A deficiency is typically reversible with prompt and adequate vitamin A supplementation. It is one of the earliest and mildest symptoms and responds well to treatment.

Who is most at risk for developing vitamin A deficiency?

Infants, young children, and pregnant women in regions with food insecurity are most at risk. Individuals with fat malabsorption disorders, such as cystic fibrosis or liver disease, are also vulnerable, regardless of their location.

What is the difference between night blindness and xerophthalmia?

Night blindness is an early symptom involving poor vision in low light, while xerophthalmia is a more severe, progressive disease characterized by severe eye dryness and damage. Xerophthalmia includes multiple stages of eye damage and can lead to permanent blindness.

What are some good dietary sources of vitamin A?

Good sources of preformed vitamin A include liver, eggs, milk, and fortified cereals. Excellent sources of provitamin A carotenoids are carrots, sweet potatoes, spinach, kale, and orange-colored fruits like mangoes and cantaloupe.

How does vitamin A deficiency affect the immune system?

Vitamin A is critical for immune function. Deficiency weakens the immune response and impairs the integrity of mucosal barriers, making individuals, especially children, more susceptible to severe infections like measles and diarrhea.

Is supplementation a better option than diet for preventing deficiency?

For most people with a healthy diet, supplementation is not necessary for prevention, as a balanced diet provides enough vitamin A. However, supplementation is an effective treatment for diagnosed deficiency and is recommended for at-risk populations in areas with high VAD prevalence.