Researchers divided more than 600 patients with Alzheimer's into three groups, one with a certain dose of vitamin E, the other with medication, and the third with a placebo. Over the next two years, compared to patients taking a placebo, patients taking vitamin E experienced a slower decline in their ability to engage in daily activities such as planning, cooking and shopping. Patients who took the drug did not achieve similar clinical effects. Therefore, researchers believe that vitamin E supplements are expected to Become a potent cure for Alzheimer's disease. If the following statement is true, which one would most challenge the researchers' conclusions? ['Vitamin E is fat-soluble, not easy to metabolize, and can cause poisoning if taken in large quantities at one time.', "Alzheimer's is an irreversible disease, and symptoms can only be delayed and cannot be reversed.", 'Vitamin E required by the normal human body can be taken from the diet without additional supplements.', 'No vitamin E is added to current anti-dementia drugs.']