Though the improvement was short-lived, another diabetes risk factor � elevation in a liver enzyme called alanine transferase � changed for the better throughout the six-month study.
Some past studies have reached similar conclusions. A recent study found that people whose diets had a healthy dose of antioxidants, including vitamin E, had a lower diabetes risk than those with lower antioxidant intakes. And vitamin E has been shown to help some people with diabetes gain better control over their blood sugar.
The new study included 80 overweight adults ages 31 to 65. Overweight and obese individuals are at increased risk of developing insulin resistance, in which the body loses sensitivity to the hormone insulin, causing blood sugar levels to rise.
Excess fat may speed the production of oxygen free radicals, potentially cell-damaging byproducts of normal metabolism. Compounding this, overweight people tend to have low levels of antioxidants, which counter the effects of free radicals. It's hypothesized that the resulting oxidative stress may contribute to insulin resistance.
The scientists randomly assigned study participants to take either vitamin E or a placebo pill every day for six months. For the first three months, the treatment group took 800 International Units (IU) of vitamin E each day, followed by 1,200 IU per day for the next three months, doses many times the recommended dietary allowance of 22 IU.
The researchers found that at both the three- and six-month marks, plasma peroxides, which are markers of oxidative stress, had fallen in the vitamin E group. After three months, blood sugar levels and insulin sensitivity had also improved, but the gains did not remain through the sixth month.
On the other hand, the researchers found a lasting decline in blood levels of alanine transferase liver enzymes, elevations of which have been tied to a heightened diabetes risk. The liver, researchers say, plays a key role in sugar and insulin metabolism, and is the main site of insulin clearance from the blood.
Vitamin E may boost insulin sensitivity and decrease diabetes risk in a number of ways, including by reducing oxidative stress to cells and by improving liver function.
However, it's unclear why blood sugar levels and insulin resistance improved only temporarily, when markers of oxidative stress and liver function continued to look better. A larger study, they conclude, is needed to clarify the picture.
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