Vitamins that are injected directly into your bloodstream, fat, or muscle tissue have a much higher rate of absorption than the same vitamins taken in pill or liquid form. For those with digestion issues and nutrient levels that are depleted because of training or other situations where the body is under stress, these are a great way to replenish vitamin levels. Check with your healthcare provider if you are currently struggling with nutrient deficiencies to see if vitamin injections can help.