The ABCs of Vitamins: What Each One Does for Your Body

By Kidney MD | Vitamins & Minerals Simplified Series

Vitamins may be small, but they play a big role in keeping your body running smoothly — from helping your heart beat to supporting your mood and immunity. Let’s break down the essential vitamins, what they do, where to find them, and when supplements might be needed.

Vitamin A

What it does: Supports eye health, skin repair, and immune function.

Where to get it: Carrots, sweet potatoes, spinach, kale, fortified dairy.

Too much can be harmful: High doses can build up in the body and harm the liver or kidneys, especially in people with CKD.

🩺 Kidney MD tip: Avoid taking extra vitamin A unless prescribed — deficiency is rare in healthy adults, but toxicity can be serious in kidney disease.

B Vitamins

There are eight B vitamins (B1 through B12), each with unique jobs.

They help: turn food into energy, support nerve function, red blood cell production, and brain health.

Vitamin	Common Name	Key Roles	Food Sources
B1	Thiamine	Energy metabolism, nerve function	Whole grains, beans
B2	Riboflavin	Red blood cell production	Milk, eggs
B3	Niacin	Supports cholesterol and skin health	Poultry, peanuts
B5	Pantothenic acid	Energy, hormone production	Mushrooms, yogurt
B6	Pyridoxine	Brain function, immune health	Bananas, potatoes, chickpeas
B7	Biotin	Hair, nails, metabolism	Eggs, nuts
B9	Folate	DNA synthesis, prevents birth defects	Leafy greens, lentils
B12	Cobalamin	Nerves, red blood cells	Fish, eggs, dairy

Who may need more:

• Vegans and vegetarians (vitamin B12)

• Pregnant adults (folate)

• People taking methotrexate (folate)

• Long-term metformin users (vitamin B12)

• Dialysis or post-bariatric surgery patients (B-complex vitamins)

  
  

🩺 Kidney MD tip: Many patients with kidney disease lose B vitamins during dialysis — renal multivitamins replace these safely without excess fat-soluble vitamins.

Vitamin C

What it does: Helps heal wounds, boost immunity, and protect cells from damage.

Where to get it: Citrus fruits, strawberries, bell peppers, tomatoes, broccoli.

Too much: In high doses, vitamin C can cause stomach upset and kidney stones (especially in CKD).

🩺 Kidney MD tip: Stick to moderate amounts (no more than 100 mg/day in advanced kidney disease unless directed).

Vitamin D

What it does: Strengthens bones, supports mood and immune health, and helps regulate calcium.

Where to get it: Sunlight exposure, fortified milk, egg yolks, salmon, tuna.

Who may need more:

• People who spend little time outdoors

• Older adults or those with darker skin

• Individuals with CKD, obesity, or malabsorption

• People taking GLP-1 medications or after bariatric surgery

  
  

🩺 Kidney MD tip: Vitamin D deficiency is common in CKD and obesity. Always check your labs before supplementing — dosing needs vary by blood levels and kidney function. It’s perfectly fine to spend time outdoors to help your body make natural vitamin D, but don’t forget your sunscreen — skin cancer risk increases with unprotected sun exposure, so enjoy the sunshine safely.

Vitamin E

What it does: Protects cells from damage, supports immunity, and helps with skin repair.

Where to get it: Nuts, seeds, vegetable oils, spinach, avocado.

Caution: High-dose vitamin E supplements can increase bleeding risk or accumulate in kidney disease.

🩺 Kidney MD tip: Get vitamin E from food rather than pills unless your clinician prescribes it.

Vitamin K – The Clotting and Bone Health Vitamin

What it does: Helps your blood clot properly and supports bone health.

Where to get it: Leafy greens like kale, spinach, broccoli, Brussels sprouts.

Special note: If you take warfarin (Coumadin) or other blood thinners, keep your vitamin K intake consistent day to day.

🩺 Kidney MD tip: Emerging research suggests vitamin K may help reduce vascular calcification in CKD, but supplements should only be taken under medical supervision.

Putting It All Together

Most people can get all the vitamins they need from a balanced diet — but certain life stages and medical conditions can make supplementation necessary.

Food First:

• Eat the rainbow (colorful fruits and veggies = diverse nutrients)

• Include whole grains, nuts, dairy or fortified alternatives, and lean proteins

• Avoid megadose supplements unless prescribed

  
  

🩺 Kidney MD takeaway:

Vitamins work best when part of a healthy lifestyle — not a shortcut for one. A tailored approach, guided by labs and clinical needs, ensures you get the benefits without the risks.