Why Is Insulin Injected Instead of Taken by Mouth?
Insulin cannot be taken orally because it would break down in the digestive process.
Insulin is a poly-peptide protein, which can be broken down by enzymes in the digestive system. By the time it reaches the small intestine, where it is absorbed, it is only a single peptide and can no longer function as insulin.
Besides the chemical reasons for not ingesting insulin, there are other reasons that have more to do with the management of diabetes.
Why Injection Is Better
Blood sugar levels are subject to great change throughout the day. What foods were consumed, exercise, stress, illness, even time of day – all of these impact glucose levels. If this were not so, there would be no need to monitor levels with a finger prick multiple times each day.
Insulin is needed to ensure that glucose is properly utilized and that levels of glucose remain stable. In order to work properly, insulin must enter the bloodstream intact.
By injecting it into the subcutaneous tissue in our bodies, it is designed to be absorbed into the bloodstream without changing its properties and within a proscribed amount of time. Insulin should not be injected directly into muscle or into the bloodstream, as both will increase the speed of absorption.
How fast absorption happens is also a function of what type of insulin is being used: rapid-acting, short-acting, intermediate-acting, long-acting or a mix of some of these. Each is designed to be absorbed and active over certain time frames, in order to cope with different glucose control needs, like consuming a meal or sleeping all night.
Possible New Alternatives
There is active research to develop alternatives to injections. One of the most promising is inhaled insulin.
There was an inhaled insulin product, Exubera, on the market for about a year between 2006 and 2007. The manufacturer withdrew it from the market because of poor sales. The product was extremely expensive, and did not provide any better results than injectable insulin.
Another potential entry into this market is called Afrezza. It is presently teetering on the edge of possible FDA approval, with a ruling currently anticipated by July 15, 2014.
These inhaled products have so far been found to be slightly less effective than injected insulin. However, the advantage of not having to inject oneself, it is believed, will increase compliance with insulin treatment. This will help prolong the health of patients.