A Complete Guide to Vitamins and Their Importance for the Human Body

Introduction

When we discuss ways to improve our health, we mostly talk about lifestyle changes and the need to exercise regularly. Although these approaches can help transform your health, we often forget how important a special group of nutrients is. We are referring to vitamins!

Vitamins are absolutely crucial for growth and maintaining good health. They function like minerals, with the main difference being that minerals are inorganic matter that we source from the earth and water, while vitamins are organic compounds found naturally in plants and animals¹.

The word ‘vitamin’ is derived from two Latin words, ‘vita’ (meaning ‘life’) and ‘amine’ (referring to ‘amino acids’). Fun fact: Initially, vitamins were incorrectly thought to be amino acids.

Vitamin H, more commonly known as biotin, is part of the B complex group of vitamins. Vitamin H is needed for healthy skin, hair, and nails. It also helps the nervous system function properly.

Dr. M.G. Kartheeka, MBBS, MD(Pediatrics)

Types of Vitamins, Their Sources, and Deficiency Symptom

There are 13 crucial vitamins, A, C, D, E, K, B1, B2, B3, B5, B6, B7, B9, and B12. They can be classified into two main types, as follows:

• Fat soluble vitamins: These vitamins are stored in the fatty tissues of our bodies. Vitamins A, D, E, and K are the four fat soluble vitamins.
• Water soluble vitamins: The other nine vitamins are soluble in water and cannot be stored in the body for long. As a result, they need to be consumed daily, and any excess is expelled from the body through urine¹. Vitamin B12, although water-soluble, is an exception to the rule. It can be stored in the liver for years.

Let’s learn the food sources, functions, and deficiency symptoms of the 13 vitamins mentioned above.

1. Vitamin A

• Sources: Cheese, eggs, oily fish, spinach, peas, milk, and yoghurt.
• Functions: Helps maintain bone health, eyesight, and immune function.
• Deficiency Symptoms Include: Dry skin and eyes, night blindness, and increased risk of infections².

2. Vitamin C

• Sources: Citrus fruits, berries, peppers, broccoli, and potatoes.
• Functions: Acts as an antioxidant, helps in iron absorption, keeps skin healthy, and helps in collagen production for wound healing.
• Deficiency Symptoms Include: Scurvy, which might cause symptoms like weakness, loss of appetite, and diarrhoea², and bleeding gums.

3. Vitamin D

• Sources: Sunlight, egg yolk, oily fish, and red meat.
• Functions: Facilitates calcium utilisation and maintaining calcium and phosphorus balance.
• Deficiency Symptoms Include: Muscle and bone pain, bone deformities in children, and may be associated with depression^2,3.

4. Vitamin E

• Sources: Plant seed oil, almonds, peanuts, peanut butter, wheat germ, egg yolk², pumpkin, and red bell pepper.
• Functions: Acts as an antioxidant and helps in immune function^2,4.
• Deficiency Symptoms Include: Muscle and nerve damage, inability to control muscle movements, and loss of sensation in the limbs⁴.

5. Vitamin K

• Sources: Leafy green vegetables, avocado, kiwi, vegetable oils², and whole grains.
• Functions: Helps in the formation of blood clots to prevent haemorrhage^2,5.
• Deficiency Symptoms Include: Frequent bruising, heavy menstrual flow, and excessive bleeding from wounds⁵.

6. Vitamin B1 (Thiamine)

• Sources: Whole grains, pork, fish, dairy products⁶, peas, bananas, oranges, liver, and nuts.
• Functions: Helps transform carbohydrates into energy.
• Deficiency Symptoms Include: Loss of appetite, irritability, muscle weakness, and blurry vision⁶.

7. Vitamin B2 (Riboflavin)

• Sources: Milk, eggs, mushrooms, green vegetables, and yoghurt.
• Functions: Helps in vitamin collaboration and helps keep red blood cells healthy.
• Deficiency Symptoms Include: Swelling of the mouth, tongue, lips, and throat, hair loss, and skin disorders⁶.

8. Vitamin B3 (Niacin)

• Sources: Saltwater fish, liver, turkey, chicken, soy, nuts, grains, and legumes^6,7.
• Functions: Helps in protein and fat utilisation⁷, also keeps skin and hair healthy.
• Deficiency Symptoms Include: Scaly skin, rashes, headache, diarrhoea, and vomiting^6,7.

9. Vitamin B5 (Pantothenic Acid)

• Sources: Mushrooms, avocados, broccoli, peanuts, chickpeas, eggs, milk, and sunflower seeds.
• Functions: Acts as an anti-inflammatory and helps in wound healing.
• Deficiency Symptoms Include: Insomnia, vomiting, stomach pain, and depression.

10. Vitamin B6 (Pyridoxine)

• Sources: Starchy vegetables, chicken, beef, noncitric fruits, and fortified cereals.
• Functions: Crucial for brain growth and function.
• Deficiency Symptoms Include: Seizures, compromised immunity, confusion, and depression⁶.

11. Vitamin B7 (Biotin)

• Sources: Sweet potatoes, avocado, salmon, eggs, seeds, and nuts.
• Functions: Helps produce vital enzymes for metabolism.
• Deficiency Symptoms Include: Diarrhoea, numbness, burning sensation, scaly skin⁶, hair loss, conjunctivitis, and lethargy.

12. Vitamin B9 (Folate)

• Sources: Spinach, nuts, asparagus, turnips, beans, whole grains, meat, Brussels sprouts, and cereals.
• Functions: Crucial for cell division and blood cell maturation.
• Deficiency Symptoms Include: Fatigue, lethargy, headache, mouth ulcers, palpitations, pallor, and anaemia⁶.

13. Vitamin B12 (Cyanocobalamin)

• Sources: Milk, cheese, eggs, and meat.
• Functions: Helps in red blood cell formation and nervous system function.
• Deficiency Symptoms Include: Tingling in hands and feet, yellow skin, swollen tongue, mouth ulcers, anaemia, and depression⁸.

There are two more compounds that resemble vitamins and function like them without being labelled as vitamins:

• Choline
• Carnitine

The Need for Vitamin Supplements

People may fall short of getting adequate amounts of all essential vitamins due to a combination of dietary, lifestyle, and individual health factors. These factors include:

• Some people could be fussy eaters who avoid certain foods due to taste or texture preferences.
• Individuals following a vegetarian or vegan diet may miss out on certain vitamins, such as vitamin B12, which is mainly found in meat, fowl or eggs⁸.
• Busy schedules may make it challenging to plan balanced meals consistently.
• Some health conditions may lead to poor absorption of certain vitamins despite adequate dietary intake⁹.
• In some cases, the amount of vitamins required by the body cannot be fulfilled through food alone.

In such situations, vitamin supplements may help support the body’s specific nutritional needs. However, you should consult a doctor before starting any vitamin supplements.

Vitamins B6, C and E along with micronutrients like zinc, selenium, iron and copper are important for maintaining a healthy immune system in an individual, repeated infections could be a warning sign of deficiency of these vitamins and micronutrients.

Dr. Ashish Bajaj, M.B.B.S., M.D. in Clinical Pharmacology and Toxicology

Precautions with Vitamin Supplements

Taking multivitamins should always be done after consulting your doctor or nutritionist. Sometimes, vitamin supplements can cause side effects when consumed in excess or even if your body reacts adversely to the ingredients of a particular supplement. Constipation and stomach pain may occur initially (usually it resolves after a few days). Excess vitamin intake can also cause severe toxicity². Read the ingredient list for any supplement you take to ensure that you are not allergic to anything in it. Also, if you have any pre-existing medical condition, you should inform your doctor before starting any new multivitamin supplement.

How to Measure Vitamin Levels?

If you think you may be experiencing symptoms of vitamin deficiency and are wondering how to check vitamin levels, these tests may need to be done after consulting your doctor:

• Vitamin D test
• Vitamin B12 test
• A complete full body checkup including vitamin D and B12 levels
• Master Full Body Checkup with vitamins

How to Interpret Test Results?

Identifying whether you have normal levels of vitamins is simple because your test results usually show columns for normal levels of vitamins and the levels in your system at the time of the test. This can help you identify if your vitamin levels are lower, higher or at par with the normal level.

For further clarity, you can ask your doctor to go over the reports.

Why is It Important to Test Vitamin Levels?

Sometimes vitamin deficiency symptoms do not show up until very late, and a test can work like a preventive healthcare check. It will let you know which vitamin you need to supplement with. Therefore, it is important to check your vitamin levels whether you are taking supplements or not.

Similarly, even if you are taking vitamin supplements, vitamin level checks are just as important to ensure that there isn’t too much of a particular vitamin in your system as that may lead to toxicity.

Tips to Maintain Good Vitamin Levels and What to Do If You Are Deficient

The strategies for managing vitamin deficiencies are essentially the same:

1. Your diet should include

• Whole grains
• Soy products
• Vegetables of all colours
• Fruits 
• Seeds and nuts
• Poultry, fish and meat²

2. Lifestyle changes

• Get some sunshine²
• People with deficiencies can also take vitamin supplements but only if they are recommended by their doctor¹.
• Be mindful of your diet. A balanced diet is often sufficient to meet your daily requirement of different vitamins. Paired with a few healthy lifestyle choices, you can easily avert major vitamin deficiencies.
• Eat balanced meals to maintain good vitamin levels and monitor them regularly with timely tests to avoid vitamin deficiency-related conditions.

Also Read: 5 Everyday Foods That Are Good for Brain Health!

Conclusion

Vitamins are vital for good health and proper functioning of the body, as they support growth, immunity, metabolism, and overall well-being. Maintaining a balanced diet rich in fruits, vegetables, whole grains, and protein sources along with healthy lifestyle habits can help avoid or manage most vitamin deficiencies. In some cases, regular monitoring of vitamin levels and taking vitamin supplements may be necessary. however, these steps should always be taken after consulting a doctor to avoid toxicity or side effects.

Also Read: Top Vitamin B12 Foods to Include in Your Diet Today!

Frequently Asked Questions (FAQs)

References

1. Vitamins and Minerals. Harvard Health. 2023. Available from: https://nutritionsource.hsph.harvard.edu/vitamins/
2. Vitamins and minerals. Betterhealth Channel. 2024. doi. Available from: https://www.betterhealth.vic.gov.au/health/healthyliving/Vitamins-and-minerals#vitamin-b
3. Vitamin D. 2025. doi. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
4. Vitamin E. 2021. doi. Available from: https://ods.od.nih.gov/factsheets/VitaminE-HealthProfessional/
5. Vitamin K. 2021. doi. Available from: https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
6. Hanna M, Jaqua E, Nguyen V, Clay J. B Vitamins: Functions and Uses in Medicine. TPJ. 2022;26(2):89-97. doi:10.7812/TPP/21.204. Available from: https://pubmed.ncbi.nlm.nih.gov/35933667/
7. Niacin. 2022. doi. Available from: https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/
8. Vitamin B12. 2025. doi. Available from: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
9. Kiani AK, Dhuli K, Donato K, et al. Main Nutritional Deficiencies. J Prev Med Hyg. 2022;63(2 Suppl 3):E93-E101. doi:10.15167/2421-4248/jpmh2022.63.2S3.2752. Available From: https://pubmed.ncbi.nlm.nih.gov/36479498/

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