8 Reasons You Feel Tired All the Time, According to Doctors

1 | Your diet is taking a toll.

Since food is fuel, it shouldn't come as a shock that your diet can have a profound effect on your energy levels. "Consuming a diet high in processed foods, sugar, and unhealthy fats can contribute to fatigue," explains Nicholas Dragolea, MBBS, a UK-based doctor who works with Noble Medical. "These foods can cause blood sugar fluctuations and lack the essential nutrients the body needs to function efficiently, leading to feelings of tiredness," he adds.

However, being overly restrictive in your diet—either nutritionally or calorically—can also leave you running on empty, especially if you develop a vitamin deficiency. Zeeshan Afzal, MD, a medical officer for Welzo, says that in particular, vitamin B12 deficiencies tend to cause fatigue and weakness. "This can be especially common in vegans or vegetarians, as vitamin B12 is primarily found in animal products," he tells Best Life.

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2 | You have a vitamin D deficiency.

Vitamin D deficiencies can also have an effect on your energy levels, experts say. In fact, "studies show that 42 percent of the US population is deficient in Vitamin D," says Kathryn Werner, MPAS, PA-C, a physician's assistant who works in psychiatry for White Pine Mental Health and Wellness.

"Levels of vitamin D that are lower than optimal can contribute to feelings of fatigue, poor sleep, feelings of sadness, and a host of other concerns," she says, adding that a simple blood draw can reveal if you're deficient. "While dietary Vitamin D and light exposure can be helpful, most people with Vitamin D deficiency require supplementation to maintain optimal levels."

3 | You're not exercising enough.

Another common cause of chronic fatigue is a lack of exercise—meaning you may be able to improve your symptoms by getting up and moving more often.

"A lack of physical activity can lead to muscle weakness and low energy levels," explains Dragolea. "Engaging in regular exercise can help improve circulation, boost mood, and increase overall energy levels, combating fatigue."

4 | Drugs and alcohol are interrupting your sleep.

Using drugs and alcohol, even in moderation, can have a depressant effect on the nervous system. "Many people think that a little nightcap will help them sleep soundly through the night. Although alcohol's sedative effects can make you drowsy, they also have other effects that can interfere with quality sleep," write experts from Harvard Health Publishing.

They explain that hours after drinking, alcohol can raise the body's level of the stress hormone epinephrine. This raises your heart rate, making you more likely to wake up throughout the night. "Indeed, alcohol may account for 10 percent of cases of persistent insomnia," they note.

5 | You have a mood disorder.

Sometimes, having a mood disorder such as depression can make you feel tired. "Chronic stress, anxiety, and depression can significantly impact energy levels, leading to fatigue. Mental health disorders may cause disturbances in sleep, appetite, and mood, which can all contribute to feelings of exhaustion," says Dragolea. In fact, a 2018 study published in the medical journal CNS Drugs points out that over 90 percent of patients with major depressive disorder report fatigue as a symptom.

Besides fatigue or insomnia, other symptoms of depression include a feeling of persistent sadness or hopelessness, a lack of interest in activities you usually enjoy, lack of concentration, and more. Speak with your doctor or mental health provider if you believe your fatigue could be the result of a mood disorder.

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6 | You're experiencing medication side effects.

If you constantly feel tired despite getting adequate sleep, your medication might be to blame. That's because fatigue is one of the most commonly listed side effects for both prescription and over-the-counter medications, ranging from antihistamines to antidepressants to beta blockers used to treat high blood pressure.

Requesting that your doctor or pharmacist review your full list of medications could help you determine whether your fatigue is a side effect, or an interaction between two or more of the drugs you take. They may be able to suggest alternatives, or alter your dosage.

7 | You have poor sleep habits.

Getting a good night's rest begins long before you lay your head down on your pillow. The Centers for Disease Control and Prevention (CDC) suggests practicing good sleep habits, also known as sleep hygiene, in order to make the most of your shuteye.

Their experts recommend sticking to a routine of consistent sleep and wake times, even on the weekends. Additionally, it's important to make your bedroom conducive to sleep: this means it should be "quiet, dark, relaxing, and a comfortable temperature." If you tend to use your electronic devices in the hours before bed, this could interfere with your sleep, the CDC adds. They suggest removing phones, computers, and televisions from the bedroom for a better night's rest.

8 | You have an underlying medical condition.

If your feeling of exhaustion persists even after getting an adequate number of sleep hours, you may have an underlying medical condition, experts say. A wide range of health conditions—anemia, diabetes, and thyroid disorders, to name just a few—can cause tiredness or fatigue. Sleep disorders such as obstructive sleep apnea, insomnia, and narcolepsy can also have a direct impact on your feelings of restfulness.

If you suspect that a medical condition could be the cause for your fatigue, keep track of any additional symptoms you may be experiencing, and discuss your concerns with your doctors.