Dangers of High Blood Sugar
The main danger of high blood sugar (hyperglycemia) is that blood sugar levels may become uncontrollable, leading to type 2 diabetes and diabetes complications that can have lifelong effects on physical, mental and financial well-being.
Overnutrition of carbohydrates and fat can lead to insulin resistance, which is when the body can no longer bring back down high blood sugar levels on its own, which it usually does by producing and responding to insulin. Prediabetics have insulin resistance, and their blood sugar levels stay above the healthy range. At this point, the individual may need to receive external insulin, but insulin resistance can be reversed with consistent lifestyle changes.
If a person with insulin resistance does not start managing their blood sugar levels, he or she can go on to develop diabetes, which is long-term high blood sugar. Diabetics have higher blood sugar levels than prediabetics because they are more resistant to insulin, and hence it is harder for them to bring back down their blood sugar levels. Diabetics commonly experience frequent urination, increased thirst and hunger, fatigue, blurred vision, dizziness, slow healing from cuts and bruises, and numbness or tingling in their hands and feet. This person is likely to become dependent on medications in order to lower blood sugar levels and to prevent further complications.
High blood sugar does not only contribute to diabetes, but also to a range of other diseases called diabetes complications. This is because excess sugar can interfere with the circulatory system and the immune system, and cause cellular stress in many different organs, resulting in damaged blood vessels, poor blood circulation, damaged nerves and cell death. In people with insulin resistance and diabetes, this damage has already occurred in the pancreas, muscle and fat cells. And if left unmanaged, the damage can spread to additional parts of the body. Common diabetes complications include stroke, coronary artery disease, diabetic foot, eye damage and kidney damage. Diabetics also have a higher risk of death from various cancers [1] and infectious diseases [2] such as COVID-19 [3] compared to non-diabetics.
Blocked Blood Vessels
The most dangerous aspect of high blood sugar is that can damage blood vessels all over the body, especially in the heart, brain, and small blood vessels. Diabetes is highly associated with diseases caused by blocked blood vessels (atherosclerosis), such as heart attack, stroke and coronary heart disease. This is because high blood sugar produces oxidative stress and chronic inflammation inside blood vessels [4,5,6]. Oxidative stress and inflammation, which are discussed in more detail here, are common types of cellular dysfunction that occur in hyperglycemia.
High blood sugar can increase LDL cholesterol levels [7] and encourage white blood cells in the blood to store LDL cholesterol inside [8]. High blood sugar also produces substances called AGEs (Advanced Glycation End-products) that encourage these abnormal, cholesterol-filled white blood cells to stick to the inner walls of blood vessels, forming plaques that block circulation [9]. AGEs further modify the physical structure of blood vessels that promote plaques, inflammation, oxidative stress [10,11].
Damaged blood vessels
In the kidneys and eyes, there are thin blood vessels that are easily damaged by exposure to high blood sugar. High glucose levels produce oxidative stress, inflammation and AGEs [12,13,14], which then damage the cells that make up the walls of blood vessels (endothelial cells). The endothelial cells can become ‘leaky’ and die [15], resulting in kidney failure and blindness. Leaky vessels in the kidney (diabetic nephropathy) cause sweet-smelling urine because the kidney is no longer able to filter sugar from urine. In the eyes, blood leaks out into the clear eyeball space and interferes with eyesight (diabetic retinopathy).
Poor blood circulation can also cause nerve damage and reduced sensation in the hands and feet, as well as slower recovery from infections. These symptoms often contribute to foot disease (diabetic foot), which is found in 6% of diabetics [16].
AGEs cause complications
Other than blood vessel damage, additional complications can arise from the aforementioned AGEs. AGEs are produced when sugar molecules chemically bind to other types of molecules such as proteins, fats and nucleic acids. They can be formed inside the body when the blood sugar level is high, or come from foods that combine carbs with proteins or fat (see here). AGEs have been shown to play a role in diabetes-related diseases in the brain and liver [17,18,19], as well as in skin condition [20], Alzheimer’s disease, Parkinson’s disease and aging [21].
Sources:
https://dx.doi.org/10.1038/s41598-020-73668-y
https://dx.doi.org/10.1016/j.numecd.2017.12.007
https://dx.doi.org/10.1016/j.dsx.2020.04.044
https://dx.doi.org/10.3390/ijms21051835
https://dx.doi.org/10.1016/j.cmet.2012.11.012
https://dx.doi.org/10.1136/heartjnl-2011-301172
https://dx.doi.org/10.1210/jc.2018-00667
https://dx.doi.org/10.1136/heartjnl-2011-301172
https://dx.doi.org/10.3390/ijms21051835
https://dx.doi.org/10.1016/j.cardiores.2004.05.001
https://dx.doi.org/10.1038/ncpendmet0786
https://dx.doi.org/10.1111/j.1368-5031.2006.00825.x
https://dx.doi.org/10.1161/CIRCRESAHA.110.223545
https://dx.doi.org/10.1161/01.ATV.0000122852.22604.78
https://dx.doi.org/10.1016/j.cmet.2012.11.012
https://dx.doi.org/10.1080/07853890.2016.1231932
https://dx.doi.org/10.4196/kjpp.2014.18.1.1
https://dx.doi.org/10.1016/j.diabres.2004.09.004
https://dx.doi.org/10.1210/jc.2007-1817
https://dx.doi.org/10.4161/derm.22028
https://dx.doi.org/10.1016/j.cmet.2018.08.014