Every cell in your body needs sugar as fuel, but it can’t use that sugar without a hormone called insulin. In a healthy person, an organ called the pancreas pumps out just enough insulin. Sugar in the bloodstream is used by the cells for energy or stored in the liver or as fat. People with Type 1 diabetes, however, cannot make their own insulin. People with Type 2 diabetes may eventually lose the ability to make insulin as well.

It doesn’t do any good to take insulin by mouth; insulin is a protein and the digestive system just breaks it down and uses the amino acids as building blocks. If you can’t make insulin, it has to be delivered to the blood stream. As a practical matter, the insulin is injected into the fat layer just under the skin, and from there diffuses into the blood stream. It has to reach the blood stream at just the right rate—too little insulin in the blood and blood sugar will skyrocket (very bad for you long-term), too much and the blood sugar can go so low that the brain shuts down. (I used this in Homecoming—the esper shock that afflicts those capable of talents like teleportation is simply low blood sugar.)

Unfortunately the rate of diffusion has nothing to do with the body’s need for insulin, either to pull down the blood sugar after eating, or to keep the cells of the heart and brain operating. There are artificial insulins available which diffuse faster or slower, and it is possible to take a very slow diffusing insulin to keep the basal metabolism (the heart, lungs, digestion, brain) going and shots of fast-diffusing insulin at mealtimes to deal with the sudden surge of sugar that digestion puts into the blood. But your metabolism varies with time of day, exercise, stress, hormones and other things, most of which are not well understood and often beyond your control.

Enter the insulin pump. Lots of people think that an insulin pump means your diabetes is really bad. Others think it’s just a convenience to keep from having to take shots, or that it does all the work for you. (It doesn’t.) None of these ideas really explains the advantages of an insulin pump.

It is true that changing the place where the pump injects insulin under your skin every three days is a lot less painful than taking five or six shots a day. And there is no question that it is easier to push a few buttons before eating at a restaurant than finding a rest room where you can load a hypodermic and expose your belly for a shot. But an insulin pump can do more than that—if you are willing to work at it.

First, the dosage with today’s pumps is much more exact than is possible with a conventional shot. With a hypodermic or an insulin pen, you can at best get the dosage to the nearest half unit. That may sound precise, but for some people half a unit of insulin is the difference between normal blood sugar and insulin shock, and a whole unit can drop blood sugar from normal to zero. Luckily even fast-acting insulin does not get into the blood as fast as glucose taken by mouth, so it is generally possible to correct for these rough dosages, but why not take the right dose to start with? Almost all of today’s pumps allow you to select the dose to within a tenth of a unit, and at least two pumps now allow even more exact dosages.

Second the basal insulin, the stuff that is dripped slowly and continuously into your system to balance your basal metabolism, can be adjusted to vary by time of day. This is not important for everyone, but some people need as much as twice the amount of insulin per hour at waking as they do when falling asleep. With long-acting insulin, this means a choice of insulin shock overnight or high blood sugar in the morning. With a properly adjusted pump, the rate of infusion of basal insulin can be adjusted in hourly or even half hourly increments.

The downsides? Insulin pumps do continue to deliver basal insulin even if your blood sugar is too low. The FDA has been worried about this. There is a pump available in Europe which when combined with a continuous glucose monitor will shut down if the wearer does not respond to a low blood glucose alarm. As far as I am concerned this is a fail-safe that increases the safety of insulin pumps, but the FDA still has not approved this feature for the USA market.

Another downside is that you have to learn to use the pump, and adjust its features to suit your own body. You will probably need to test your blood sugar more frequently, up to fifteen times a day. Some people are freaked out by the idea of being continuously connected to a machine, even one smaller than a deck of cards. And if you don’t have a waterproof model swimming and even bathing can cause problems.

Is it worth it? Yes, especially for those who are insulin sensitive or for those whose need for insulin varies quite a lot over the course of a day. But you do have to be prepared for a lot of work to get it working as it can.

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