Different Needs

• Humans and dogs need different amounts of vitamins. Human supplements could contain more or less of a particular vitamin than your dog requires.
  
  

Unnecessary Vitamins

• Vitamins such as A and C are produced naturally in a dog's body and are not as important to supplement. Supplements for humans may contain more of these vitamins than your dog requires.
  
  

Age is a Factor

• How many vitamins your dog needs is dependent on age. Older dogs don't consume as much food and absorb fewer nutrients, making vitamin supplementation more necessary.
  
  

Harmful Supplements

• Supplements designed for humans with too much iron can cause liver damage in dogs. According to veterinarian Dr. Holly Nash, dogs require 36.4 mg of iron per pound of food consumed.
  
  

Overdose

• Fat-soluble vitamins such as A, D, E and K are stored in a dog's fat cells for future use. These vitamins present a greater risk for overdose, as opposed to water-soluble vitamins such as C and B. Watch for fat-soluble vitamin levels when giving your dog supplements.
  
  

In the End

• Ultimately, the nutritional needs of dogs and humans are separate and require separate vitamins. Stick with supplements formulated for dogs, and your pet will lead a healthy life. If you have specific questions about your dog's particular needs, consult a veterinarian.