Dear Doctor: I'm a 78-year-old woman who developed shingles in December 2014. The rash settled in the nerves on my left side, from under the breast, to the waist and around the middle of my back. Is there anything I can take to ease the pain? Would the vaccine help?

Dear Reader: Shingles is a reactivation of the herpes zoster virus -- the virus that causes chickenpox. When people contract chickenpox, usually as children, the virus makes its way along their sensory nerves, ending up at the nerve cells along the spine. The virus then sits within the cells in a dormant state. It can stay there for the rest of a person's life and not cause problems, with the body's immune system keeping the virus in a dormant state.

However, when immunity decreases, the virus can replicate within a nerve cell, following a particular nerve pathway to the skin and creating a rash along that pathway. The most common risk factor for developing shingles is age, with 80- to 89-year-olds having 10 times greater risk compared with those 10 years old and younger.

The nerve pain created by shingles can be very severe and can persist even after all the lesions have disappeared. The pain can be burning, sharp or stabbing and can worsen with even the lightest touch. When the pain lasts for more than four months, the diagnosis is termed "postherpetic neuralgia." That's the pain syndrome you have.

There are many medications for postherpetic neuralgia. Tricyclic antidepressants like amitriptyline, nortriptyline and desipramine work to decrease pain signals from the skin to the central nervous system. However, they're often not well-tolerated in older patients and can lead to sedation, dry mouth and worsening memory. They would not be my first choice for you.

Gabapentin (Neurontin) and pregabalin (Lyrica) work directly through the nerves to decrease pain. Gabapentin causes much more drowsiness compared to pregabalin, so many of my patients who have difficulty sleeping at night due to the pain of postherpetic neuralgia do well with it. However, because people with symptoms that also occur during the day often can't tolerate the sedating effects of gabapentin, I switch many of these patients to pregabalin; although this drug can cause drowsiness, it is better tolerated. The anti-seizure drug valproic acid also can significantly decrease pain.

Capsaicin, the active component of chili peppers, is known for irritating the sensory nerves, but perhaps remarkably, can lead to pain relief when used in cream form for those with postherpetic neuralgia. Note that you must apply capsaicin multiple times per day, and for many people, the burning, stinging sensation is intolerable.

Opiates also can relieve the acute pain, but when used long-term, they can cause tolerance and addiction.

As for the vaccine, although you had shingles more than two years ago, it could still reduce the risk of future episodes. However, no vaccination studies have been done in patients who have already had shingles, so the potential benefit is unclear. In addition, the vaccine won't reduce your current nerve pain.

In summary, I recommend speaking to your doctor about medications like gabapentin or pregabalin and whether to get the shingles vaccine to perhaps decrease the risk of future episodes.

(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: I've always had headaches, from the time I was a teenager. But now I get them more often -- about one headache per week. Is this a warning sign of something?

Dear Reader: Headache is among the most common -- and ancient -- of physical complaints. You would be hard-pressed to find someone who hasn't suffered from a headache at some point in time.

Mentions of headache in written texts date back to 1200 B.C., and treatments over the centuries have included the use of leeches, garlic, oil in the ear, tying a dead mole to one's head (no, we're not making this up), magnets, electricity, psychotherapy and that universal refuge, the soothing bath.

Most headaches are periodic bouts of pain centered in the head and/or neck. It's not the brain tissue itself that's sending pain signals -- it's the surrounding tissues, blood vessels and nerves that serve the area. Many headaches respond to medication and lifestyle changes. Some, however, like migraines, may persist despite treatment. Some headaches can be warning signs of larger problems such as blood clot, stroke or tumor. Thankfully, those are rare.

Although there are many different types of headache, most fall into four major categories:

-- Tension headaches are the most common, marked by dull pressure, like a band tightening around your forehead.

-- Sinus headaches, which cause a deep, throbbing pain, occur when the cavities around the cheeks, nose and forehead become inflamed.

-- Cluster headaches, marked by severe pain in and around one eye, get their name because they often occur in clusters, but they are less common.

-- Migraines, which can last for hours or even days, cause debilitating pain, often on one side of the head. They can be accompanied by flashes of light, photosensitivity, a blind spot in the field of vision, tingling sensations on the skin and nausea.

Headaches can also be the result of factors such as eye strain, allergy, hunger or fasting, fever, fatigue, dental problems, lack of fluids and hangover, to name just a few. The truth is, the subject of headache is vast and extremely complex. And despite many strides forward (remember that dead-mole-on-the-head cure?), science still has more questions than answers.

What signals that a headache may be something to worry about?

-- A major change to the pattern of your headaches, such as going from a few per month to one per day.

-- The sudden onset of persistent headaches, particularly after age 50.

-- A headache that is the most severe you have ever had.

-- The onset of a headache after a traumatic event to the head.

-- Any headache that alters cognitive function, is accompanied by fever and a stiff neck, or includes symptoms like slurred speech, blurred vision, weakness, numbness or seizures.

These can be signs of underlying conditions such as head injury, infection, tumor, high blood pressure, fluid buildup in the skull, decrease in blood flow or bleeding in the brain.

This all sounds alarming, so let us assure you again that these conditions are rare. However, if any of the above happen to you, please be safe and seek immediate care.

(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: I'm hearing that vitamin D can reduce the risk of colds and flu -- and that more foods should be fortified with it. What's the evidence for that?

Dear Reader: As a doctor, I'll confess I'm skeptical about such a broad claim. As I wrote in a prior column, vitamin D is not so much a vitamin as a hormone within the body. It's produced by the body and, further, many foods are rich in the substance. If your vitamin D levels are normal, ingesting additional vitamin D wouldn't seem to help prevent the common cold.

That's not to say such thinking is new. The famed English general practitioner Robert Edgar Hope-Simpson, noting that the influenza virus occurred predominately in the winter, surmised that lack of exposure to the sun may make people more susceptible to influenza. He also noted that in tropical climates, influenza occurs more often during the rainy season when there is a decrease in exposure to the sun. To produce vitamin D, the human body needs sun exposure, so the purported connection between vitamin D and colds seems to have started with that correlation.

Further, a deficiency of vitamin D can lead to decreased white blood cell function, impeding the body's ability to fight off infection. Additional vitamin D stimulates the production of antimicrobial peptides.

As for scientific research on the topic, a 2012 study of 30 patients with chronic lung disease and very low levels of vitamin D (less than 10 ng/ml) showed a 43 percent reduction in exacerbations of the disease when they were given 100,000 units of vitamin D monthly (average 3,200 units per day) for one year. Commonly, these exacerbations are related to infection. A 2015 study showed similar findings of a 43 percent reduction in moderate to severe exacerbations among lung disease patients with vitamin D levels below 20 ng/ml.

However, vitamin D supplementation did not change the upper respiratory infection rate. Also, in both studies, vitamin D supplementation had no effect on people with normal vitamin D levels, i.e., greater than 20 ng/ml.

In another 2012 study, patients with normal vitamin D levels were randomized to receive 100,000 units of vitamin D or a placebo monthly for 18 months. The authors concluded that there was no difference in the rates, or the severity, of upper respiratory infections between those who took vitamin D and those who took a placebo.

The latest study, to which I believe you are referring, was a combined analysis of 25 studies from around the world, including Afghanistan and Mongolia. This analysis linked vitamin D supplementation to a 12 percent reduction in the number of people who developed at least one respiratory infection.

However, in further analyzing the data, the authors found that most of the benefit for vitamin D supplementation was seen in those with levels less than 10 ng/dl, which is very low. The authors did not find any statistical benefit in vitamin D supplementation among people with levels greater than 10 ng/ml. The authors also found that daily or weekly intake of vitamin D had a greater benefit than larger doses given monthly.

In summary, vitamin D does seem to have benefits in decreasing colds and flu in those who have exceedingly low levels of vitamin D -- numbers not seen in the majority of the population. Further, patients with chronic illnesses, elderly people and residents with long, cloudy winters may find that vitamin D supplementation can decrease the frequency of upper respiratory infections.

(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.)