Dear Doctor: I recently sent my mom an email at midnight, and ever since then she's been after me to stop using my smartphone at bedtime. She insists that the light from the screen interferes with sleep patterns. Is that really true?

Dear Reader: I'm pretty sure this isn't the answer you're looking for, but your mother is right. The ways in which the "blue light" emitted by smartphones, tablets and computer screens affects sleep patterns is quite a hot topic in scientific circles these days. And according to the scores of studies done in recent years, the answer is consistently the same: Yes, these devices do have a negative effect on your nightly rest.

This is troubling because insufficient sleep is associated with serious conditions such as high blood pressure, diabetes, coronary heart disease, depression and even obesity. About one-third of all Americans don't get the seven hours of sleep that are recommended to maintain good mental and physical health. In fact, the sleep deficit in the United States is so severe that the Centers for Disease Control and Prevention now identify it as a public health problem.

So how do the multiple screens in our lives figure into the epidemic of insufficient sleep?

Light is the cue your brain relies on to sync itself with the outside world. It regulates your circadian rhythms, which influence sleep patterns, hormone releases, body temperature and other vital functions.

Smartphones, tablets and computers all emit high-energy light in the blue spectrum. This particular wavelength, which is similar to sunlight, has been shown to suppress the release of melatonin, a hormone produced by the pineal gland in the brain that makes you feel sleepy.

When you use your smartphone at night, even up to 90 minutes before you go to sleep, you're confusing your body clock. The blue light from the screen is telling your brain it's still daytime. That suppresses the release of melatonin, which makes it difficult for you to fall asleep.

Once you do drift off, the disruption to your circadian rhythm is profound enough that it's difficult to stay asleep. What sleep that you do manage to get is often of poor quality. Instead of feeling refreshed when you wake up, you face the day tired.

Some smartphone makers have introduced an option to move the self-illuminated screen from bright blue to a warmer yellow/red spectrum, as with Apple's "Night Shift." And while this may a have modest effect on sleep, we would recommend that putting your phone away at bedtime is a better idea.

To give yourself the best chance at a good night's sleep:

-- Read from a printed book rather than an illuminated screen.

-- Make your bedroom as dark as possible. Use curtains to block exterior light, and eliminate inside light from clock dials, TV sets and, yes, smartphones.

-- Do what you can to block out sound -- earplugs or a white noise machine can help.

-- Keep your bedroom cool; 65 to 68 degrees is ideal.

-- Steer clear of large meals before bedtime.

-- Be aware that caffeine and alcohol can interfere with sleep.

Remember -- how you feel during the day has a lot to do with how well you slept the night before.

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)

Dear Doctor: I just entered my second trimester without any nausea at all. Considering a recent study linking morning sickness to a successful pregnancy, should I be worried?

Dear Reader: Nausea occurs in up to 80 percent of pregnancies. The cause appears to be related to a rapid increase of the pregnancy hormone beta hCG (BHCG) as well as the rise of estrogen. The nausea can be distressing for many women and can lead to worries about a future miscarriage.

Paradoxically, nausea may be an indication of a successful pregnancy. Preliminary studies have found this correlation, but they could not differentiate if the lack of nausea was related only to an early miscarriage or to an overall successful pregnancy.

A 2016 study in JAMA Internal Medicine looked at women between the ages of 18 and 40 who had a history of one or two miscarriages and who were trying to conceive. Of those women who were deemed to be pregnant based on a measurement of BHCG, 797 eventually became pregnant. These women kept daily diaries, recording instances of nausea and vomiting from the second week to the eighth week of their pregnancy. If a woman had nausea once, she was considered to have nausea in the pregnancy.

In week two of their pregnancy, only 20 percent of the women reported nausea, but by week eight of their pregnancy, nearly 85 percent of women had reported nausea. After the eighth week of the pregnancy, nausea was measured at monthly intervals. Also, to confirm a viable pregnancy, the women underwent an ultrasound at week six or week seven.

Investigators found that women who experienced nausea at some point during their pregnancy had a 50 percent reduction in the risk of a miscarriage. Those women who were afflicted with both nausea and vomiting at some point in their pregnancy had a 75 percent decrease in the chance of having a miscarriage. Moreover, based on the week-six and week-seven ultrasounds, the lack of nausea in the women who miscarried was not related to a lack of a viable pregnancy.

The authors proposed that nausea during pregnancy may have a protective effect by alerting a woman about her condition so as to alter her diet and avoid toxic substances, which could increase nausea or harm a pregnancy. I'm not so sure about this, but it is a possibility.

In regards to this study, I can understand the worry about your lack of nausea as you enter the second trimester of your pregnancy. But when you look further at the study, you find that nearly 94 percent of miscarriages happened in the first trimester of the pregnancy. So as you enter the second trimester, there is significantly less likelihood that you will have a miscarriage. Also, this study focused on women who had previously had a miscarriage, so its findings may be less applicable to you.

In summary, I wouldn't be concerned about your lack of nausea. But please do schedule follow-ups with your obstetrician for your regular prenatal care.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)

Dear Doctor: My parents, who are in their late 70s, are both now using hearing aids. This makes me wonder -- when should a hearing test become part of an annual checkup?

Dear Reader: Our ears connect us to the world, and yet until something goes wrong, hearing is one of the senses we seem to take for granted.

It's a good idea to have a hearing test as a baseline when you're a relatively young adult so that if you develop a hearing issue later, you will have a useful comparison. You can talk to your family doctor about giving you a hearing test or seek out the help of a hearing professional, known as an audiologist.

Hearing loss usually happens so gradually that you may not even be aware of it. It's not until you run into problems such as frequently asking people to repeat themselves or cranking up the volume on your TV that you realize something has changed.

Hearing is a complex process. When you hear a sound, your brain is interpreting electrical signals that it receives via the auditory nerve. These signals originate in the delicate structures within your inner ear, which receive sounds -- that is, vibrations -- and turn them into nerve impulses.

It's important to identify hearing loss as soon as possible. Studies suggest a link between hearing loss and serious conditions such as depression or dementia. An early diagnosis and successful intervention can reduce symptoms of depression and help preserve cognitive function.

If you think you may have trouble with your hearing, you're not alone. About 15 percent of American adults report some form of hearing problem. Signs that you could be experiencing hearing loss may include:

-- Frequently asking people to repeat themselves;

-- Having trouble pinpointing the source or direction of a loud noise;

-- Trouble hearing telephone conversations;

-- Being told the volume of your TV or radio is excessively loud;

-- Difficulty understanding a person who isn't facing you as he speaks;

-- Struggling to hear conversations in noisy environments, like a restaurant;

-- Difficulty understanding high-pitched voices;

-- Being told by others that your hearing seems impaired.

If you've experienced these situations, a hearing test is a good idea. It will reveal whether you have hearing loss in either ear, and pinpoint the type of hearing loss and to what degree it has progressed.

There are several types of hearing tests.

A physical exam with an instrument called an otoscope reveals any problems in your ear canal or eardrum. Additional tests include a pure tone test, which reveals how well you can hear -- you guessed it -- a variety of pure tones.

A speech test evaluates your ability to understand the spoken word. Tympanometry tests reveal any problems in the middle ear and evaluate the mobility of your eardrum.

These hearing tests are painless. Taken together, the results offer a detailed picture of your hearing, known as an audiogram. And if a problem should be uncovered, your audiogram gives you and your doctor the information needed to move forward.

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)