How Long Does It Take Blood Sugar To Drop?

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The American Diabetes Association (ADA) recommends in the establishment of glycemic goals, age may be a consideration with targets for preprandial, bedtime/overnight, and hemoglobin A1c (HbA1c) levels [1] 

The statement includes a new pediatric glycemic control target of HbA1c of less than 7.5% across all childhood age groups. The adult HbA1c target is less than 7% [2,3].  To obtain those goals, premeal blood glucose levels should be in the range of 80–130 mg/dL. 


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People with repetitive episodes of severe hypoglycemia, cardiovascular disease, complications such as retinopathy or neuropathy, substance abuse, or untreated mental illness may need higher targets to keep the HbA1c less than 8% and preprandial glucose levels need to be in the range of 100-150 mg/dL.

Those patients dependent on insulin should test blood glucose daily before meals, 1-2 hours after meals periodically, and at bedtime. When this is not possible, patients should try to obtain 2-4 measurements each day, including fasting (premeal) levels and at bedtime.

Other useful tests include dipping strips for urine ketones especially when the following symptoms develop:

  • Any illness like a cold or the flu
  • Nausea, vomiting, or abdominal pain
  • Excess urination/thirst
  • An unexpected high blood glucose level
  • Rapid fluctuations in the degree of hyperglycemia

Types of Insulin Based on Speed of Action in Lowering Blood Glucose

Rapid-acting insulins include lispro, glulisine, and aspart insulin. They have a rapid onset of action (5-10 minutes), a short interval to peak action (45-75 minutes), and a short duration of action (2-4 hours). This makes them suitable prior to eating. In addition, NPH insulin will not inhibit the action of insulin lispro when the 2 agents are mixed together before injectiing which is not the case for regular insulin.

 Short-acting insulin includes regular insulin. After subcutaneous administration, its onset of action occurs in 0.5 hours, peaks at 2.5-5 hours, and its duration of action is 4-12 hours.

The standard strength of regular insulin is 100 U/mL (U-100), but 500 U/mL (U-500) insulin is increasingly used, but primarily in those with Type 2 diabetes.

Both regular human insulin and rapid-acting insulin are effective at lowering postprandial hyperglycemia. Rapid-acting insulin might be slightly better at lowering HbA1c [4].  

Intermediate-acting insulins include NPH insulin and provides a slower onset and longer  duration of  action than regular insulin does. The onset of action usually occurs at 1-2 hours, peaks int 4-12 hours, and the lasts about 14–24 hours.

Long-acting insulins include insulin glargine and insulin detemir (Levemir). Insulin glargine produces a relatively stable level with no peak and lasts more than 24 hours. In some cases, it can produce a stable basal serum insulin concentration with a single daily injection, but if patients require lower doses. then two injections are given. Insulin glargine and insulin detemir should not be mixed with any other form of insulin.

Common Insulin Regimens

The goal of treatment in type 1 DM is to provide insulin in a range that mimics the body. Insulin replacement therapy is accomplished by giving a basal (baseline) insulin and a premeal insulin. The basal insulin is either long-acting (glargine or detemir) or intermediate-acting (NPH). The preprandial insulin is either rapid-acting (lispro, aspart, or glulisine) or short-acting (regular).


Common insulin regimens are:

  • Split or mixed – NPH with rapid-acting such as, lispro, aspart, or glulisine or regular insulin before breakfast and dinner
  • Split or mixed variant – NPH with rapid-acting or regular insulin before breakfast, rapid-acting or regular insulin before supper, and NPH before bedtime
  • Multiple daily injections (MDI) – A long-acting insulin such as glargine or detemir once a day in the morning or evening (or twice a day in some patients) and a rapid-acting insulin before meals or snacks adjusting the dose according to the carbohydrate intake and the blood glucose level
  • Continuous subcutaneous insulin infusion (CSII) – Rapid-acting insulin infused continuously 24 hours a day through an insulin pump at 1 or more baseline rates, with additional boluses (units) given before each meal and more doses administered if blood glucose levels exceed target levels 

In healthy people, the HbA1c (glycosolated hemoglobin) level is lower than 6% of the total hemoglobin. Hemoglobin is the oxygen carrying component of red blood cells responsible for the red color of blood. A level of 6.5% signals the presence of diabetes. Complications of diabetes can be delayed or prevented if the HbA1c level can be kept below 7%. HbA1c is not dependent on any particular measurement of blood glucose. It represents the past 6-8 weeks of glucose levels in the blood.

Postprandial blood sugar is the glucose level in the blood either 1 or 2 hours after a meal

Influence on HbA1c is dependent on the overall glucose control over 6-8 weeks not one measurement such as fasting or postprandial.


When should you check? Before meals, 2 hours after meals periodically, at bedtime

What is an ideal reading? 80-120, up to 150 is fine

Why your readings might be too high? Not enough insulin, too much food (calories in the form of sugar), less activity

What to do if your readings are too high? Supplement with regular insulin

Can you Inject and eat immediately? Yes

How fast does insulin lower blood sugar? Depends on the speed or onset of action Blood sugar targets throughout the day are 80-150


  1. [Guideline] American Diabetes Association. Standards of medical care in diabetes--2011. Diabetes Care. 2011 Jan. 34 Suppl 1:S11-61.
  2. [Guideline] Chiang JL, Kirkman MS, Laffel LM, Peters AL. Type 1 Diabetes Through the Life Span: A Position Statement of the American Diabetes Association. Diabetes Care. 2014 Jun 16. [Medline].
  3. Tucker M. First-Ever ADA Guidance Specifically for Type 1 Diabetes. Medscape Medical news. Available at Accessed: June 20, 2014.
  4. Garg S, Ampudia-Blasco FJ, Pfohl M. Rapid-acting insulin analogues in Basal-bolus regimens in type 1 diabetes mellitus. Endocr Pract. 2010 May-Jun. 16(3):486-505.

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