It is clear that taking a multivitamin and eating a nutritious diet are key to achieving optimal health, but taking too many vitamins may not be a good idea. The New York Times Health Guide points out that "high doses of certain vitamins can be poisonous." Less dangerous but perhaps more insidious is the fact that taking too many vitamins could make you feel sleepy.
In order to function properly, your body needs certain amounts of all vitamins every day. There are many types of vitamins, and each has its individual function. According to The New York Times Health Guide, "You can develop health problems [deficiency disease] if you do not get enough of a particular vitamin." The best way to find out if you are lacking a vitamin is to schedule an appointment with your doctor and tell him that you want to have a full checkup.
The idea that everybody needs the same amount and types of vitamins per day is not accepted by all medical experts. Thenutritionreporter.com says "such broad-brush nutritional standards have inherent defects. Roger Williams, Ph.D., a preeminent scientist, developed the concept of 'biochemical individuality' to describe how people's differences in anatomy, biochemistry and genetics greatly influence their individual nutritional requirements. Williams argues that RDA-type recommendations were based on an unrealistic statistical norm, not the complexities and variations of real people."
Several vitamins may induce annoying and debilitating side effects, especially when taken in large doses. According to the 1stholistic.com, vitamin A can cause anorexia, headache, blurred vision, loss of hair, bleeding lips, cracking and peeling skin, muscular stiffness and pain, severe liver enlargement and damage, anemia, fetal abnormalities (pregnant women must be very careful), menstrual irregularities, extreme fatigue, liver damage, injury to the brain and nervous system. Calcium can cause drowsiness, extreme lethargy, impaired absorption of iron, zinc and manganese, calcium deposits in tissues throughout body and the mimicking of cancer on an X-ray, but some people experience weakness, fatigue, exacerbation of hypertension, increased activity of anticoagulants at 1,000 I.U., while some research shows that as little as 300 I.U. can slow down the immune system."
According to The New York Times Health Guide, "The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid."
Ultimately, vitamins can make you sleepy—or at least lethargic, drowsy and fatigued. Accordingly, you may want to use care when ingesting calcium and vitamins A and E or consider discussing your diet needs with a doctor.