If you feel tired often, you are not alone. The Sleep Foundation reports that 40% of people feel sleepy enough during the day to interfere with regular activities. The reasons for feeling tired are many. Some are obvious, such as having interrupted sleep at night, an old mattress that hurts your back or working different shifts.

Not all reasons for being tired are that obvious, though. Here are five causes that you may not realize can make you tired.

1. Vitamin Deficiency

Even if you get 7-8 hours of sleep every night, you can feel fatigued due to a lack of vitamins. One of the most common is iron-deficiency anemia. It affects 25% of the population.

Many people lose the ability to absorb vitamin B12 as they age. Vitamin B12 is responsible for oxygen and energy delivery, so a lack of it can cause fatigue.

Surprisingly, more than half the world’s population is deficient in vitamin D. A deficiency in this vitamin has also been linked to fatigue.

Typically, once vitamin levels are restored, the symptoms of fatigue can go away. Your doctor can recommend a vitamin supplement or find out if you have an underlying cause for vitamin deficiency.

2. Medical Conditions

Some chronic conditions can cause fatigue. Ask your doctor if an underlying health problem plays a role in your tiredness. You may require hypothyroidism, diabetes, depression or Guillain Barre Syndrome treatment. Other conditions linked to fatigue include kidney disease, cancer, fibromyalgia and anxiety disorders.

Being tired a lot doesn’t mean you have a serious disease. However, a visit to your doctor can help ease your mind and rule out these causes.

3. Unhealthy Body Weight

People who are overweight are more likely to develop obstructive sleep apnea, which causes fatigue during the day. Excess weight can also lead to other health conditions that cause fatigue, such as diabetes, heart disease and depression.

Poor sleep quality and lack of sleep are also linked to weight gain. If people don’t sleep well because they are overweight, and they are overweight because they don’t sleep well, it can end up being a downward cycle of unhealthiness. Talk to your doctor if you think your weight may affect your sleep pattern.

4. Too Much Caffeine

If you depend on caffeine to stay awake, you may wonder why too much of it causes people to feel tired. While caffeine gives you a temporary energy lift, consuming too much of it or drinking it too late in the day can interrupt your sleep cycle. This pattern causes you to feel tired the next day. Your sleepiness may cause you to reach for the coffee, setting you up for a cycle of fatigue.

Green tea and other caffeine-containing drinks are good for your health, so you don’t necessarily need to cut caffeine altogether. Try cutting back and avoiding it in the afternoon to see if your sleep patterns improve.

5. Processed Food

Most people understand that overeating processed food is unhealthy. Foods high in sugar and refined grains can lead to obesity, diabetes and heart problems. However, eating high amounts of processed food can also cause you to feel sleepy.

When you eat a diet high in refined grains and sugar, you may miss out on protein and other nutrients. Your body begins to break down muscle and fat to create energy, causing you to feel tired. Your insulin levels and blood sugar can go higher, leading to fatigue.

Adding fish, eggs, whole grains, fruits and vegetables to your diet while cutting back on sugar and refined grains can help you feel more energetic.

6. Allergies

Watery eyes, a stuffy nose and tiredness are common symptoms of allergic rhinitis. Your doctor can help you find a plan to treat your allergy symptoms to have more energy. You may need medication and a plan to avoid the allergens.

Being tired all the time is no fun. You and your doctor can work together to find out the underlying cause of your fatigue and put you on the path to an energetic future.