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Coffee and Blood Glucose in Mice

Researchers recently investigated (see summary in http://www.sciencedaily.com/releases/2010/06/100609111316.htm) in laboratory mice whether or not coffee prevented the development of high blood sugar (hyperglycemia). The mice used in this experiment have a mutation that makes them become diabetic.

Study: A group of 11 mice were given water and another group of 10 mice were supplied with diluted black coffee (coffee:water 1:1) as drinking fluids for five weeks. The composition of the diets and living conditions were similar for both groups of mice. Blood glucose was monitored weekly for all mice. After five weeks, there was no change in average body weight between groups. Results indicated that blood glucose concentrations increased significantly in the mice that drank water compared with those that were supplied with coffee. Finally, blood glucose concentration in the coffee group exhibited a 30 percent decrease compared with that in the water group.
1. What was the hypothesis of this experiment? (Reminder: Hypothesis is a statement.) What question(s) was (were) the investigator asking?
2. Which is the control group? Why?
3. Which is the treatment group? Why?
4. Did the researchers follow the scientific method in their experimental design? Explain.
5. Do you think that there may be any possible biases or other problems in this experiment? Explain.
6. Based on the data, was the hypothesis supported, and what can you conclude from this experiment?

Reference: Yamauchi et al. (2010). Coffee and caffeine ameliorate hyperglycemia, fatty liver, and inflammatory adipocytokine expression in spontaneously diabetic KK-Ay mice. Journal of Agricultural and Food Chemistry, 58 (9), 5597-5603. May 12, PMID: 20405946, ISSN: 1520-5118.

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The hypothesis is the "best guess" that the experimenters have for what will happen in their experiments. Let's say that I dose my mice with morphine and then have them perform cognitive tasks. My hypothesis would be that, compared to mice with no morphine on board, the mice given morphine would perform the task slower and less well.

In this case, the experiment tests the effects of caffeine given orally. Their control is non-caffeine fed mice. The measured variable is blood glucose levels. As a result, it can be said that their hypothesis is that caffeine would reduce blood glucose levels. Again, keep in mind that a hypothesis is a statement, so in that sense, it is different from a research question (e.g. what effects does caffeine have on blood glucose levels?) The authors actually wrote this in their research question within the last paragraph of their introduction:

"In this study, we first examined whether the ingestion of coffee would prevent the development of hyperglycemia in KK-A y mice. Second, we investigated the mechanism of action of coffee on the pathogenesis of type 2 diabetes in KK-Ay mice. Subsequently, to identify the compound contributing to the antihyperglycemic effect, we attempted to clarify the preventive effect of caffeine on the development of hyperglycemia."

You could essentially take that and rewrite it into a hypothesis. Let's take their first research question, for example, and rephrase it into: "the ingestion of coffee prevents the development of hyperglycemia in KK-Ay mice."

The control group, as listed in the question, is the water fed mice that, besides not receiving caffeine ...

Solution Summary

The following problem discusses an experiment that investigated the effect of coffee on blood sugar in rats. This solution explains the experiment in 1058 words.