Saturday, November 26, 2011

Zinc and Insulin

In the last thirty years, the antibodies associated in medical minds with type 1 diabetes have changed considerably. I wrote about, a while back, a person who'd written a book about health care, whose daughter had been diagnosed with diabetes and tested for antibodies at the same hospital that I was, Children's Memorial Hospital in Chicago, some twenty years before me. At the time of his daughter's diagnosis, just like at the time of my diagnosis, it was standard practice to test for antibodies- but the antibodies being tested for were different. Different antibodies have continually been added and subtracted from the diabetes antibody tests because the newer antibody tests are found to have better specificity and sensititivity.
His daughter was tested for bovine milk antibodies, which are certainly found in the type 1 diabetes population at higher levels than in the general population, but not in a very dramatic way; it nonetheless pointed to a possible cause of diabetes, to know that those antibodies are more common. I was tested for insulin antibodies (why those would cause diabetes is pretty straightforward), Glutamic Acid Decarboxylase antibodies (GAD coats the islet cells), and Islet Cell Antibody 512 (another easy name). I was positive for the latter two.

I was diagnosed only five years ago, but there's already been a change to the classic antibody panel done for type 1 diabetes. The new antibody tested for has a descriptive name: it is ZnT8, which stands for Zinc (Zn) Transporter (T) 8 (the 8th type of zinc transporter, the one responsible for insulin- see wiki blurb. The name does indeed point to something that is found in abundance in the pancreas and in the islet cells.

Zinc has been known to be a part of insulin for more than eighty years. I just read a very informative article on the state of knowledge of the relation of zinc and diabetes written in 1936. The article is an evaluation of certain insulin addititives, particularly zinc and protamine, and analyzes the amount of zinc in various insulins for sale at that time.

Anyways, as it happens, zinc is important to everybody, and its functions matter to the development of most cases of diabetes. Zinc deficiencies, which affect between a third and a fourth of all people worldwide (a smaller portion in the food secure part of the world) causes insulin resistance, probably because the body needs zinc to make insulin. Mutations of the zinc transporter gene can result in various forms of diabetes. Autoimmune attacks on the zinc transporters is a better predicter of the development of type 1 diabetes than any other antibody currently known.

All of us who inject insulin are also injected zinc and one thing I found myself wondering when I was fairly newly diagnosed was, do we inject a significant amount of zinc? Can we overdose on the zinc in our insulin? Studies seem to suggest that diabetics, including type 1s, generally don't have enough zinc, so the answer clinically is probably not. But here's another way to look at it.

The recommended daily allowance of zinc for adult men and women are 11 mg and 8 mg per day respectively. The amount required for toxicity is between 20 mg and 40 mg per day.

Let's pretend you inject 100 units of insulin per day. How much zinc are you injecting?
100 units of insulin with nothing added contains roughly 0.015 mg zinc- maybe a little more, but definitely nowhere near your daily requirement of zinc.
But most of the insulins on the market have a little zinc added. If you took 100 units of Lantus, you'd be getting 0.045 mg zinc from the Lantus. With Levemir, 100 units would get you 0.08 mg of zinc, and 100 units of Novolog of Novolog would get you roughly 0.03 mg of zinc. With NPH you'd be getting about 0.035 mg zinc. Apidra and Regular have no zinc added at all, so all you'd be getting is the endogenous 0.015 mg of zinc.
So, even if all of your insulin was Levemir, and you were a woman taking 100 units of Levemir per day, you'd be getting just under 1% of your daily zinc requirement from your insulin.

You'd have to have some really heavy duty insulin resistance to be getting a significant percentage of the RDA of zinc through insulin injections- unless! injected zinc does more than oral zinc. I know of no evidence of this though.

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