According to the National Sleep Foundation, there's no specific number of hours people must sleep. Amounts vary from person to person and can change based on age, health and even temporary circumstances. For example, you might need to sleep more if you're coming back from a very active day or if you're particularly stressed or sick.
According to the Ohio State Comprehensive Cancer Center, anemia -- characterized by low numbers of functional red blood cells -- can cause extreme fatigue, muscle weakness, dizziness and mental fatigue. This can cause you to sleep longer, as your body might be trying to fight the fatigue. However, sleeping too much when you're anemic can actually cause you to feel even more tired during the day. Make sure you're getting an uninterrupted night of sleep and take a 20-minute nap during the day if necessary. Deficiencies in iron, folic acid and vitamin B-12 can all cause anemia. Talk to your doctor to see if you need supplements to treat your anemia.
Just because you're spending a lot of time in bed doesn't mean you're actually resting. If you keep waking up throughout the night, then your body won't be rested and you'll need to sleep more to make up for the many times you're waking up. One cause could be restless leg syndrome, a condition that causes unpleasant sensations in the legs as you lie or sit still, resulting in an urge to shake or move your legs. Iron deficiency is thought to be one risk factor for RLS.
If you're sleeping too much and still feeling tired during the day, you might have a vitamin D deficiency. A serious vitamin D deficiency can cause fatigue, depression and muscle weakness, all of which can lead you to sleep too much. Although your doctor can prescribe vitamin D supplements, the best source of this vitamin is the sun. Daily exposure for as little as 10 minutes should do the trick. Consult your doctor if the condition persists, though. People with dark skin -- or people who wear sunscreen -- as well as people suffering from digestive disorders or obesity face a higher risk of vitamin D deficiency.
Sleeping Too Little
The National Sleep Foundation states that there's no proven danger in sleeping too much, but there is danger in sleeping too little. In laboratory studies, people who sleep less than four or five hours a day can suffer from changes in mood and performance. They are also more likely to get sick, as their immune system suffers from the lack of sleep. If you're sleeping more than usual, however, and you can't trace it to an obvious cause such as overwork or a stressful situation, check with you doctor: you might have a nutrient deficiency.