SINCE injectable insulin was first used in 1922 to lower the blood sugar levels of diabetics, it has saved millions of lives. In large enough doses, however, insulin is a deadly poison.
Injection of one-tenth of a millilitre would cause your blood sugar to drop enough to leave you shaky, sweaty and unable to concentrate, though you would soon recover. Half a millilitre would probably render you temporarily unconscious, and 10 millilitres would almost certainly be fatal.
One reason insulin kills is that the brain, unlike the rest of the body, can only function on one energy source: glucose. If blood glucose levels drop too low for too long, the brain dies. Yet it is the body’s attempt to battle low blood sugar that is probably the most common cause of insulin-induced death. If sugar levels fall dangerously low, the body produces massive amounts of adrenalin and other hormones that convert stored glycogen in the liver back into glucose. This burst can cause a heart attack, especially in the old or weak.
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Death from an accidental overdose of insulin is nevertheless extremely rare. For a start, you have to be injected with it, and a fatal dose would fill 20 insulin syringes. And insulin works slowly, giving you 20 minutes or so to call for help. Even many hours after the onset of coma, sugar is all that is needed for a complete recovery.
“Insulin works slowly, giving you about 20 minutes to call for help”
Insulin has been involved in its fair share of murder cases, however, many of which are documented by Vincent Marks and Caroline Richmond in their book Insulin Murders (RSM Press, 2007). An insulin-induced death leaves no obvious traces for a normal autopsy to pick up. Even if foul play is suspected, insulin is tricky to test for. The method used in live patients – checking for low blood sugar levels – doesn’t work on a dead body because its individual cells can continue metabolising glucose for hours or even days after death, so all corpses have low blood sugar.
There have been more than 50 documented cases in which insulin has been used by murderers – mostly involving victims too weak to resist injection or cry for help. The first was in Yorkshire, UK, in May 1957, when nurse Kenneth Barlow injected around 0.8 millilitres of insulin into his wife’s buttocks to incapacitate her, before drowning her in the bath. California hospital attendant William Dale Archerd was found guilty in March 1968 of using insulin to murder his nephew and two of his seven wives. And British nurse Beverly Allitt used insulin to murder at least four children in her care in 1991.
If insulin is sounding like a useful murder weapon, beware. Forensic teams are increasingly alert to its use, and methods to test for it in corpses, including immunoassays and mass spectrometry, are better than ever.
