Sorbitol is a sugar alcohol which is unable to be utilised by the human body and can take a long time to be removed from the body once it is there. If too much sorbitol builds up in the body, it can deplete vital nutrients and cause damage to organs including the eyes, nerves, kidneys and blood vessels, resulting in conditions like diabetic retinopathy, diabetic neuropathy and diabetic nephropathy. When sorbitol is in the bloodstream, it attracts excess water, causing swelling of the cells which leads to mechanical damage.
We encounter sorbitol in two ways. Sorbitol is used as an artificial sweetener in many foods and beverages marketed to diabetics or those concerned about sugar intake and small amounts are also naturally present in some fruits such as apples, pears, peaches and prunes. The human body can make sorbitol as part of the glucose metabolism process, through the action of an enzyme called aldose reductase, which has an accelerated action in people with high blood sugar.
As PCOS frequently progresses into diabetes, this is something that women with PCOS need to be aware of.
There has been some effort by pharmaceutical companies to develop a drug to prevent sorbitol accumulation in the body, however, they have not made any significant progress due to severe side effects. Some studies in the late 1990s, however, have shown significant positive results with reducing sorbitol levels through vitamin C supplementation.
Vitamin C appears to inhibit the enzyme aldose reductase, which converts glucose to sorbitol.
The first study, published in 1994, examined the effect of ascorbic acid supplementation on the sorbitol levels found in the red blood cells of young adults with type I diabetes. The subjects had a baseline sorbitol level twice the recommended amount, despite being deemed to consume an adequate amount of vitamin C in their diet and having normal levels of ascorbic acid in the plasma component of their blood. They were given either 100 mg or 600 mg of ascorbic acid for 58 days. By the 30th day of the study, subjects taking both doses of vitamin C had their sorbitol levels returned to normal, independent of changes in their blood sugar control, which was generally moderate to poor throughout the study period, according to fasting blood sugar levels and HbA1c tests. This means that the effect that vitamin C has on sorbitol levels is independent of blood glucose levels.
In the second study, published in 1999, the researchers confirmed in test-tubes that increasing concentrations of glucose increased the amount of sorbitol contained in red blood cells and that vitamin C reduced the action of the aldose reductase enzyme in red blood cells. They found that at concentrations above 100 micromoles, vitamin C reduced sorbitol production by around 30 percent. When the concentration of vitamin C was increased to between 600 and 900 micromoles, it reduced sorbitol production by almost 50 percent.
The lower level of vitamin C concentration is achievable at normal dietary intake levels, however, to attain the higher concentration of vitamin C in the plasma and red blood cells, supplementing with between 1,000 and 1,500 mg per day would be required.
More Information:
Cunningham JJ, Mearkle PL, & Brown RG. (1994) Vitamin C: an aldose reductase inhibitor that normalizes erythrocyte sorbitol in insulin-dependent diabetes mellitus.Journal of the American College of Nutrition, 13(4), 344-50. PMID: 7963139
Vincent TE, Mendiratta S, & May JM. (1999) Inhibition of aldose reductase in human erythrocytes by vitamin C. Diabetes research and clinical practice, 43(1), 1-8. PMID: 10199583
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