Why/how does high blood sugar levels cause fatigue/sleepiness/fatigue?

[WeRSauron]

This is a simple question, but for me, a diabetic, an entirely puzzling and important question: how or why does high blood sugar levels cause fatigue/tiredness/sleepiness?

Even minutes after I eat, I feel really tired and sleepy. When my bloog sugar gets high I can hardly keep my eyes open. That’s when I need to take some stimulant to keep me awake and alert. (I usually take a caffeine pill.) This is especially dangerous when I have to drive - falling asleep at the wheel is very unsafe. A number of times I have had to pull over and rest for a while or risk actually falling asleep at the wheel.

Why does this happen? How does it happen? It’s not always after eating, either, so I suppose it’s not about food or digestion but more pointedly about bloog sugar levels. If anyone can help demystify this, I shall be forever grateful.

WRS

[KarlGauss]

The phenomenom you describe is neither generally appreciated nor well understood.

Here is an abstract from a very recent article (Oct 2004) on the subject (the full text of the article is not available for free).

Here is a quote from that paper (with the relevant references):

Diabetes is associated with rapid fluctuations in blood glucose. Hyperglycemia is a frequent consequence of the relative or absolute insulin deficiency that is intrinsic to diabetes, and hypoglycemia is a common side effect of treatment with insulin and some antidiabetic medications (1). Because the brain is dependent on a continuous supply of glucose as its principal source of energy, changes in blood glucose concentration rapidly affect cerebral function. The adverse effects of acute hypoglycemia on cognitive function and on mood are recognized (2,3). However, less is known about the effects of acute hyperglycemia on cerebral function. Anecdotal descriptions by patients with diabetes suggest that when blood glucose is elevated, changes in mood (such as increased irritability and feelings of diminished well-being) occur and rapid thinking is more difficult.

Published data on the effects of acute hyperglycemia on cognitive function are contradictory. Two studies (4,5) have demonstrated impaired language skills and reduced IQ during hyperglycemia compared with euglycemia. Other studies have shown no effect of acute hyperglycemia on cognitive function (6-8) or mood (9). However, in the study by Gschwend et al. (6), only two tests were used to assess cognitive function, and in the studies by Draelos et al. (8) and Weinger et al. (9) the study cohorts had chronically poor metabolic control, which may have allowed cerebral adaptation to occur in response to prevailing high blood glucose concentrations.

1. Tattersall RB: Frequency, causes and treatment of hypoglycaemia. In Hypoglycaemia in Clinical Diabetes. Frier BM, Fisher BM, Eds. Chichester, U.K., John Wiley and Sons, 1999, p. 55-89
2. Deary IJ: Effects of hypoglycaemia on cognitive function. In Hypoglycaemia and Diabetes: Clinical and Physiological Aspects. Frier BM, Fisher BM, Eds. London, Edward Arnold, 1993, p. 80-92
3. Heller SR, Macdonald IA: The measurement of cognitive function during acute hypoglycaemia: experimental limitations and their effect on the study of hypoglycaemia unawareness. Diabet Med 13:607-615, 1996
4. Holmes CS, Hayford JT, Gonzalez JL, Weyderl JA: A survey of cognitive functioning at different glucose levels in diabetic persons. Diabetes Care 6:180-185, 1983
5. Davis EA, Soong SA, Byrne GC, Jones TW: Acute hyperglycemia impairs cognitive function in children with IDDM. J Pediatr Endocrinol Metab 9:455-461, 1996
6. Gschwend S, Ryan C, Atchison J, Arslanian S, Becker D: Effects of acute hyperglycemia on mental efficiency and counterregulalory hormones in adolescents with insulin-dependent diabetes mellitus. J Pediatr 126:178-184, 1995
7. Hoffman RG, Speelman DJ, Hinnen DA, Conley KL, Guthrie RA, Knapp RK: Changes in cortical functioning with acute hypoglycemia and hyperglycemia in type 1 diabetes. Diabetes Care 12:193-197, 1989
8. Draelos MT, Jacobson AM, Weinger K, Widom B, Ryan CM, Finkelstein DM, Simonson DC: Cognitive function in patients with insulin-dependent diabetes mellitus during hyperglycemia and hypoglycemia. Am J Med 98:135-144, 1995
9. Weinger K, Jacobson AM, Draelos MT, Finkelstein DM, Simonson DC: Blood glucose estimation and symptoms during hyperglycemia and hypoglycemia in patients with insulin-dependent diabetes mellitus. Am J Med 98:22-31, 1995

Here is another relevant abstract.

[chula]

When I asked my doctor this question years ago, she laughed out loud and said it was not possible for sugar to make me feel fatigued/sleepy/fatigued. I have since done some research and have come up with the following understanding of hypoglycemia: excessive sugar intake causes my body to overproduce insulin and crash to a low blood sugar level. I have no expertise in this area and would be happy to be corrected.