If you're feeling tired all the time, the cause may be related to a condition, your diet, or your sleep patterns, among other possibilities.

If you find yourself tired all the time, you may suspect a sleep disorder. And while that’s a wise place to start, there may be other reasons for your daytime tiredness.

“Fatigue and sleepiness are two different things,” explains clinical psychologist Jennifer Martin, PhD, David Geffen School of Medicine at UCLA. “Sleepiness means you’re not getting enough good quality sleep, and during the day you can’t keep your eyes open. Fatigue is not having a lot of energy. You can feel that way from having chronic pain, stress, or exercising too much.”

Tired All the Time? Consider These Possible Culprits

cause of your fatigue could stem from a number of conditions that may be worth checking out, from anemia to an underactive thyroid to a urinary tract infection. Here, we look into the possible reasons you may feel tired all the time.

Is Anemia the Reason You’re Tired All the Time?

Anemia, also known as having a low red blood cell count, can cause fatigue, shortness of breath, and headaches.

In addition to having lower-than-normal amounts of red blood cells, the cells may not have enough hemoglobin, an iron-rich protein that helps circulate oxygen around the body. Common causes of anemia include deficiencies in iron, folate, or vitamin B12. Food rich in these nutrients can help correct the problem.

A blood test can reveal whether you have anemia. Mild or severe, it should be treated.

Is an Underactive Thyroid Causing Your Daytime Tiredness?

The thyroid gland, which produces a hormone that affects metabolism, is involved with how the body converts food to energy. Hypothyroidism is the medical term for an underactive thyroid. When food metabolizes too slowly, the result can be fatigue.

Hypothyroidism affects women more than men, and it’s more common inn people over the age of 60. How is hypothyroidism diagnosed? A physician will take a full medical history and then perform blood tests to check thyroid function and hormone levels. The condition is treatable with medications.

The Foods You Choose Can Make Your Tired

Not eating enough, and eating the wrong foods (highly processed foods and sugary foods such as donuts) won’t provide the nutritional fuel you need to power through the day, which can lead to feeling tired. Combining protein with a complex carbohydrate not only helps you stave off hunger, but it helps to energize both body and brain.

“Some patients tell me they get tired after eating certain foods,” says Dr. Martin. “If you eat something that makes you tired, don’t eat it. Likewise, if you eat something at night that keeps you awake, avoid that food.”

The Link Between Depression and Feeling Tired All the Time

It’s commonly thought of as a mental and emotional disorder, but depression also has physical symptoms, including headaches, loss of appetite, and fatigue.

One of the most common disorders in the United States, depression can take hold at any age. In older adults, depression can occur in tandem with other serious chronic conditions.

Being depressed drains energy. Medications sometimes can help resolve the fog of depression, but side effects can include fatigue. Always report any medication side effect to your physician, as there may be other options to try.

Urinary Tract Infections

Urinary tract infections (UTIs) are among the most common infections. Women are more likely to get them, but men, especially as they get older, can be more prone to UTIs as well.

Itching and/or burning while urinating are the most typical symptoms of a UTI, but older adults also are more likely to feel weak, shaky, and tired, while sometimes exepriencing muscle aches as well. “Any infection can make people feel tired,” says Dr. Martin. “It can cause both fatigue and sleepiness. It’s also harder to get good sleep because you may have pain or other symptoms from the infection.”

Is Dehydration the Culprit?

Not getting enough fluids can lead to fatigue. While the general rule of thumb has been eight 8-ounce glasses of water per day, it may be different for you. If you sweat a lot, you’ll need more.

Simply hiking outdoors on a hot humid day can cause you to perspire more than you think. Drink water before such an outing or a hard workout like tennis. Depending on how long you are at the activity, it may help to drink a little during your activity as well. You know you’re well-hydrated when urine is light in color. (See also our post “How Much Water to Drink?“)

What Else Can Make Us Feel Tired?

There are many other medical conditions such as heart and lung diseases, diabetes, and fibromyalgia—not to mention medications—that can cause fatigue. Sometimes, trying a different medication or taking it at a different time of day may solve the problem. Either way, it’s a good idea to see your physician to help you address your tiredness.

Originally published in 2017, this post is regularly updated.