Dear Doctor: My 16-year-old daughter is normally very sweet and accommodating. But when she's hungry, she becomes a completely different person. I think she can control her mood when she's hungry; she insists she can't. Who's right?

Dear Reader: Not only is the hunger-related crankiness you're describing a real thing, it's prevalent enough to have recently earned an entry in the Merriam-Webster dictionary. According to the official definition, your daughter is "hangry." As the dictionary puts it, hangry is "a clever portmanteau of hungry and angry, and an adjective that describes being irritable due to hunger." But why?

When it's been too long between meals, there's more going on than just that hollow feeling and a stomach rumble. The real action takes place in the brain, which like the rest of the body, uses glucose to function. In fact, the nerve cells of the brain, known as neurons, are so plentiful and active that they use half of all of the glucose we take in each day. Wait too long between meals, and blood glucose levels drop. When this happens, the brain, which plays a role in virtually every vital function that keeps us alive, lets us know. And not in a polite, "Ahem, I'm a bit peckish, can we maybe eat sometime soon?" kind of way. With that blood sugar drop, the brain sets in motion a cascade of biological processes that basically shout: FOOD! NOW! I MEAN IT!

Specifically, when blood sugar drops to levels the brain finds inadequate, it triggers the release of cortisol and epinephrine. Known as counterregulatory hormones, they act against the effects of insulin and raise levels of blood glucose. Also involved in the complex hunger response is something called neuropeptide Y, which contributes to the physical sensation of emptiness.

In addition, cortisol and epinephrine are so-called stress hormones and are associated with increased levels of aggression. So is neuropeptide Y. So as blood sugar levels drop, the biochemicals released to increase the fuel available to the brain are also paving the way for us to feel stressed and angry. Some researchers theorize that this is no accident. While neuropeptide Y is busy making us feel empty, cortisol and epinephrine are making sure that nothing will come between us and finding that next meal that the brain so desperately needs.

In experiments exploring the hunger-anger nexus, researchers from the University of North Carolina at Chapel Hill found a connection between hunger and negative emotions. Participants looked at images that were either positive, negative or neutral. They were then shown a Chinese pictogram. Those who were hungriest, and who had previously viewed a negative image, were the most likely to feel negatively toward the pictogram. Those who reported lower levels of hunger didn't have the same level of negativity. Still, another experiment bolstered your "you can control your hanger" point of view. When participants were asked to be aware of their emotions, the hungry ones experienced less hanger.

So you and your daughter are both right. Hanger is real, and for some people, it can be controlled.

(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. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My son and his wife have a 13-month-old son, born at home, whom they refuse to have vaccinated. In fact, the only time he's seen a doctor was a month ago when he had a bad cold. How can I convince them of the merits of vaccination?

Dear Reader: Our human lives have diverged significantly from that of our ancestors, meaning everyday existence is much more controlled and mechanized than ever before. It is thus understandable to want to live and raise one's children in a more "natural" way -- and to have control over our lives when so much is governed by the society around us. This conflict is evidenced by many parents' reaction to vaccine guidelines for children.

Your son and daughter-in-law may feel that these vaccines are harmful and unnecessary. But, if you ask generations who saw the ravages of polio or the infant deaths from pertussis, there would be no question as to the benefits of vaccines. Consider:

Polio: Prior to the development of a vaccine, polio led to thousands of deaths and even more cases of paralysis in this country alone. The illness has no cure, so the best option is to be vaccinated.

Measles: Before there was a vaccine, more than 90 percent of children acquired measles by the age of 15. In the decade prior to 1967, when the vaccination became widespread, 48,000 children were hospitalized for measles each year; 1,000 developed permanent brain damage; and 500 died. Since the vaccine, the number of measles cases has dropped 99 percent.

Mumps: Prior to routine vaccination in the late 1960s, this was a very common illness, affecting about 186,000 children per year. For most children, it was mild, but if the virus invaded the brain, children could develop irreversible hearing loss. Further, in males, if the virus affected both testes, chronic sterility ensued. Routine vaccination has reduced the incidence of the disease by, again, 99 percent.

Rubella (German measles): Prior to widespread vaccination against rubella, a disease transmitted from pregnant woman to fetus, an epidemic in the early to mid-1960s caused 2,100 deaths in utero; 11,250 spontaneous abortions; and more than 20,000 babies born with a syndrome that leads to hearing loss, heart disease, vision loss, liver dysfunction and developmental delays.

Pertussis: This disease, known as whooping cough, was also devastating, with a high mortality rate.

That's not to say all vaccines are perfect. Some can cause Guillain-Barre syndrome, which can have devastating neurologic consequences. They can also lead to inflammatory reactions such as hives and breathing problems. But these side effects are very rare -- and are significantly dwarfed by the benefits of vaccination to the individual and to the general population. There is no evidence that vaccines lead to autism, as many people believe.

Because vaccination has largely eradicated many of the above diseases, an unvaccinated child may have a lower likelihood of getting the illnesses. But the more people refuse vaccination, the greater the risk to individuals and the general public.

I understand that it's difficult for you, knowing that your grandson isn't vaccinated. All you can do is to provide your son and daughter-in-law with the evidence of the benefits of vaccination. It's up to them to make the decision.

(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. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My doctor offered to prescribe sleeping pills because I'm under a lot of stress at work and am suffering from insomnia. I'm tempted, but the side effects scare me. How often do people sleepwalk or binge-eat or do other activities after taking sleeping pills? I even heard that one woman drove across the country!

Dear Reader: When it comes to having trouble getting a good night's sleep, you're not alone. It's estimated that at least one-third and perhaps up to one-half of all Americans experience some kind of sleep problem. These range from the occasional sleepless night to the chronic -- and at times debilitating -- insomnia that affects up to 10 percent of the U.S. population. To deal with this unwanted wakefulness, an estimated 9 million Americans now turn to sleep aids of one kind or another. And considering the complex physiological mechanisms that regulate sleep, it's not that surprising that there would be some side effects associated with these medications.

The medications most commonly associated with the odd behaviors you mentioned are zolpidem, sold under the brand name Ambien, and eszopiclone, sold under the brand name Lunesta. They fall into a class of drugs known as hypnotics. These work by binding to certain receptors in the brain, which affects neural activity in a way that allows the user to slip into sleep.

Although the majority of users experience few if any side effects, some people have reported a range of peculiar and potentially dangerous behaviors that they had no memory of taking part in. These include waking up with food or dirty dishes in their beds, then finding a mess in the kitchen that indicated they had prepared a meal sometime during the night. Other anecdotes include a man waking up in the family car in his pajamas, parked miles from home with no idea of how he got there. A woman reported receiving clothing deliveries from a $2,200 online shopping spree she had no memory of, and another woman woke up shivering in a bathtub filled to the brim with cold water and surrounded by burning candles.

As we mentioned, these side effects are considered to be rare. The labels of the relevant drugs now carry prominent warnings that, while under the influence of the medication, it's possible to walk, eat or even drive and have no memory of it afterward. Also carried in the warning labels is the possibility that varying levels of cognitive impairment, as well as physical symptoms like headache, nausea and a bad taste in the mouth, can persist into the following day.

While the temporary respite these sleep aids can offer from a bout of insomnia is helpful, it's important to note that they are not intended for long-term use. Rather, they are meant for occasional use, to help someone who is struggling with sleeplessness to get through a rough patch. However, because the drugs are quite effective and also potentially habit-forming, it's possible to become dependent on them over the long term. If you do decide to try them, please keep that -- and the label warnings -- in mind.

(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. Owing to the volume of mail, personal replies cannot be provided.)