— Anon.

Answer: Obstructive sleep apnea (OSA) is very common (15% to 30% of men in the United States and 10% to 15% of women), but there are still many people who aren’t diagnosed. Although it is more common in people who are overweight or obese, it can occur in people of any weight. They might have something about the anatomy of their airways that causes their airways to close during sleep.

There are many consequences of untreated OSA, and all of these are more likely with more-severe obstruction. Because people with OSA don’t sleep well, they are at a higher risk for motor vehicle accidents. Memory problems and depression are some of the most common complications.

Heart disease, especially in the right side of the heart, is much more likely, and high blood pressure, coronary artery disease, and heart failure are also more likely. Diabetes is more common and independent of the weight effect. For all of these reasons, it’s important to make a diagnosis and treat this condition quickly.

CPAP delivered by a mask and a compressor is the usual first-line treatment. It has been shown in several studies to be more effective than most other therapies. It prevents the airway from closing and allows a person to keep breathing during sleep.

However, it is undeniable that many people have trouble adjusting to the mask. Nasal pillow masks tend to be tolerated better. I recommend that my patients try several different types of masks and to be patient with the device before considering alternatives.

Prior to considering surgery, oral appliances can be considered during a consultation with a person’s dentist. A hypoglossal nerve stimulation device can time an electrical impulse to the tongue with inspiration and improve your air flow.

Overall, the effectiveness of surgery at reducing OSA by at least 50% ranges from 30% to 80% in different studies.

Dear Dr. Roach: I am 24 years old and have extreme fatigue. Many tests haven’t given an answer. I did have a stool test that showed a parasite called Giardia lamblia. Could this be the cause of the fatigue?

— W.A.

Answer: Giardia lamblia is an intestinal parasite that is present all over the world. The disease is transmitted by direct exposure to the parasite, such as in contaminated open water, for example. It’s a common cause of traveler’s diarrhea.

Although some people with Giardia have no symptoms, many people will develop symptoms 7-10 days after exposure. Diarrhea and other gastrointestinal symptoms are common with acute Giardia, with about 66% of people noting weight loss.

Without treatment, acute giardiasis can progress to chronic giardiasis. There is less diarrhea, but the weight loss can be profound — 10% to 20% of a person’s body weight. The fatigue and malaise can be overwhelming. Furthermore, the parasite can interfere with the absorption of nutrients, especially vitamin A, vitamin B12 and folic acid.

Fortunately, now that you have a diagnosis, there is effective treatment. Single-dose tinidazole is more than 90% effective, but nitazoxanide and metronidazole are other options.

Contact Dr. Roach at ToYourGoodHealth@med.cornell.edu.