DCB Newsletter #1/23: DID YOU KNOW… that insulin enables you to think, grow and reproduce?

When one thinks of diabetes, insulin automatically comes to mind, an important hormone for the human metabolism. But what is its function and, above all, what side effects does insulin have?

Besides lowering glucose being the main task for insulin, there’s more to it. While usually unnoticed, in type 1 diabetes, where insulin is missing, these side-functions become evident:

1. Cognitive function, learning, memory

Insulin has a key role in the hippocampus, a brain region that is highly involved in learning, memory and cognitive performance. Besides that it has regulating connections to the limbic system, where emotions, motivation, motor-action control and social behavior is controlled. An absence of insulin (and therefore glucose) leads to difficulties in memory, cognitive function and irritability. The higher the insulin sensitivity, the higher the cognitive performance indicators. [1]

2. Hunger and satiety

Physiologically, after a meal containing carbohydrates, insulin levels rise. As insulin passes the blood-brain-barrier, it acts as a strong feedback signal on satiety-centers (specifically, POMC-Neurons) in the hypothalamus. An absence of or resistance to this signal, as in T1/T2 diabetes, is interpreted by the brain as a shortage in nutrients and energy, thus leading to more appetite and initiating food seeking behavior. [2]

3. Tissue growth

Insulin is one of the most important anabolic, growth hormones. Especially muscles and bones, but also skin, hair and nails depend on the presence, and the right amount of insulin to grow. [3]

4. Fertility

Insulin acts on the female reproductive tract by regulating the production of estrogen and testosterone in hormone-producing cells on ovaries. High insulin levels can lead to high testosterone production, leading to symptoms of PCOS (irregular periods, masculine hair growth, acne). Also contributing to excess estrogen production, sore breasts, fibroids and heavy menses are typically associated with high levels of insulin. Conversely, the absence of insulin (as in T1D) is interpreted as a shortage in food-supply and in order to preserve energy, specific brain centers stop the production of cycle-regulating hormones, leading to irregular periods and infertility. [4][5][6]

Thanks so much for reading and we’ll provide you with the next episode of this series soon!

[1] Capucho AM, Chegão A, Martins FO, Vicente Miranda H, Conde SV. Dysmetabolism and Neurodegeneration: Trick or Treat? Nutrients. 2022; 14(7):1425. https://doi.org/10.3390/nu14071425

[2] S.M. Anika, T.R. Houpt, K.A. Houpt, Insulin as a satiety hormone, Physiology & Behavior, Volume 25, Issue 1,1980,Pages 21-23, ISSN 0031-9384, https://doi.org/10.1016/0031-9384(80)90175-4.

[3] Insulin and bone health in young adults: The mediator role of lean mass Torres-Costoso A, Pozuelo-Carrascosa DP, Álvarez-Bueno C, Ferri-Morales A, Miota Ibarra J, et al. (2017) Insulin and bone health in young adults: The mediator role of lean mass. PLOS ONE 12(3): e0173874. https://doi.org/10.1371/journal.pone.0173874

[4] Fica S, Albu A, Constantin M, Dobri GA. Insulin resistance and fertility in polycystic ovary syndrome. J Med Life. 2008 Oct-Dec;1(4):415-22. PMID: 20108521; PMCID: PMC3018970.

[5] Hill JW, Elmquist JK, Elias CF. Hypothalamic pathways linking energy balance and reproduction. Am J Physiol Endocrinol Metab. 2008 May;294(5):E827-32. doi: 10.1152/ajpendo.00670.2007. Epub 2008 Feb 19. PMID: 18285524; PMCID: PMC5724360.

[6] George B. Karkanias, Jose C. Morales, Chang-Sheng Li, Deficits in Reproductive Behavior in Diabetic Female Rats Are Due to Hypoinsulinemia Rather Than Hyperglycemia, Hormones and Behavior, Volume 32, Issue 1, 1997,Pages 19-29, ISSN 0018-506X,