It is probably safe to take 2-4 mg per day, but doses of 35 mg per day are toxic. Possible Adverse Effects Doses larger than 1,000 IU a day are not recommended. High consumption of vitamin D can raise the levels of calcium in the blood to dangerous levels and can result in calcium being deposited into internal organs. 5 Vitamin K Contraindications People using anticoagulant drugs such as Warfarin or Coumadin should not take vitamin K. 5 Iron Possible Adverse Effects Iron supplements are a leading cause of fatal poisonings in children. Adults should keep iron tablets in a locked cabinet out of reach of young children.
Iron deficiency is the most common nutrient deficiency in the United States.
The groups at highest risk are infants under two years of age, teenage girls, pregnant women and the elderly. Extreme fatigue is a primary symptom of anemia, the last stage of iron deficiency. However, iron overload can result in heart disease, infection and possibly even cancer. 5 Iron supplements, therefore, should only be used when tests show a deficiency exists. 4 Magnesium Contraindications People with kidney disease or severe heart disease should not use magnesium supplements except under a physician's supervision.