Dear Doctor: Which pain reliever is safer -- acetaminophen, ibuprofen, celecoxib or naproxen? It seems as if they all carry some risks.

Dear Reader: Pain is a symptom to which we can all relate. It's also an important indicator of possible injury within the body and should be acknowledged, not simply by taking medication, but also by understanding the cause of the pain. That said, one person's pain is different than another's, with some people needing greater pain relief.

So, if you need a medication for pain, what should you use? Let's look first at acetaminophen (Tylenol). Acetaminophen has been used since 1955; it is available in multiple products, works well for pain, and is for the most part safe. However, at high doses -- specifically, above 4,000 milligrams a day, or eight tablets of Extra Strength Tylenol -- the medication can cause liver damage, or even death, especially in those who are malnourished, drink alcohol in excess or consistently take more than 4,000 mg per day. Age is also a factor, as those over 40 have a greater risk of liver failure and death after over-dosage.

Ibuprofen (Advil, Motrin) has been used for pain since 1974. It is one of many medications classified as non-steroidal anti-inflammatory drugs (NSAID). NSAIDs work by inhibiting formation of mediators of pain and inflammation, and they're notably effective at decreasing inflammation in swollen joints related to arthritis.

Naproxen (Aleve) was first marketed in 1976 and works similarly to ibuprofen. But it has a longer half-life, giving it a longer-lasting effect. Both ibuprofen and naproxen decrease the formation of prostaglandins in the stomach. These chemicals produced by the body have hormonelike effects, protecting the stomach lining from acidity. The decrease of prostaglandins can injure the stomach lining, leading to stomach inflammation, ulcers and possibly severe bleeding.

Celecoxib (Celebrex) is a more selective NSAID and does not decrease prostaglandins in the stomach. This translates into significantly less likelihood of creating ulcerations.

All NSAIDs also reduce prostaglandins in the kidneys, which can lead to kidney injury. This injury becomes worse in people who have a history of chronic kidney disease, who are older, or who have congestive heart failure or cirrhosis.

Lastly, the chronic use of high-dose NSAIDs has been linked to an increased risk of heart attacks. Celecoxib may have a slightly greater risk of this than ibuprofen and naproxen, but a recent New England Journal of Medicine study looking at those who used NSAIDs chronically for arthritis found no difference in cardiovascular events between celecoxib and either ibuprofen or naproxen.

Of the drugs you listed, my feeling is that acetaminophen is the safest when used regularly. However, I would use acetaminophen at no higher doses than 4,000 mg per day and, if you were to use it regularly, I would recommend decreasing this amount to 2,000 to 3,000 mg per day.

The NSAIDs -- ibuprofen, naproxen and celecoxib -- are needed by some who have inflammatory arthritis, and they are good medications in the short-term. I would caution against consistent long-term use, especially at high doses and especially if you have any history of heart disease.

(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 memory is terrible. To be honest, it always has been. I seem to spend half my time searching for my keys or wondering whether I forgot to turn off the stove and lights. Could memory training help?

Dear Reader: Ready for a short answer that you're not likely to forget?

Yes.

As long as problems with recall do not arise from either medical or physiological issues, it is indeed possible to improve one's memory. And it's not just a matter of mastering complex systems or relying on clever tricks. An intriguing study published in the scientific journal Neuron shows that a certain type of memory training has a measurable and lasting effect on networks that connect different regions of our brains.

Researchers compared the brain activity of 23 top memory athletes with 23 people with no memory training at all. After just six weeks of training, scans of the brains of the amateurs began to resemble those of the memory athletes.

The training focused on a strategy known as "method of loci," also sometimes called the memory palace. The idea is that you mentally "place" things you want to remember -- a person's name, where you put the phone bill, what your spouse asked you to pick up at the store -- into a landscape you know really well. Then when you picture yourself moving through that landscape, you'll encounter the items you wanted to remember.

What was striking about the study wasn't just that the amateurs significantly improved their memories. In the months after learning and adopting the method of loci technique, the new pathways created in their brains were still there.

That's all pretty high-octane stuff. But science shows that maintaining a good memory is a whole-body endeavor, and that simple lifestyle changes can make a difference.

Here at UCLA, we have a memory program for adults with known risk factors for cognitive decline. These risk factors include being sedentary, being overweight, having diabetes or having a family history of Alzheimer's or dementia. Studies show that stress and depression can also have a hand in memory issues.

Participants in the UCLA program improve their diets and are asked to exercise regularly and work on stress reduction. They also do brain training, some of it quite similar to the regimens reported in the Neuron study. They make a point of memorizing the kind of information that we now relegate to our electronic devices, such as a shopping list, frequently called phone numbers, birthdays of family and friends, addresses, and one or two credit card numbers.

At the end of 12 weeks, participants reported improvements not only to their memories, but also to their moods and general sense of well-being. They enjoyed the challenges of shopping without a list and skipping the autodial feature on their phones to make calls themselves.

Perhaps a similar memory program is available in your area. And even if not, an improved diet, more exercise and basic memory practice are changes that you can incorporate into your own life.

(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: What are the benefits of apple cider vinegar? I hear about it on social media, but I don't understand how vinegar can lead to weight loss or help me control my blood sugar.

Dear Reader: My mom is a big proponent of apple cider vinegar. She likes to put it on her salads and vegetables, or just drink a spoonful of it. I am somewhat dubious about her claims of its health benefits, but I am also skeptical of my own resistance to accepting her belief.

Vinegar is created by the fermentation of many natural substances, including grapes, sugar cane, rice and, in this case, apples. The fermentation process produces acetic acid of various concentrations. With apple cider vinegar, the acidity is fairly high -- at a pH of about 3 on a scale of 0 to 14 (a pH of 1 to 7 is acidic).

Apple cider vinegar also contains many polyphenols, or plant-based compounds. These antioxidant compounds have been shown to decrease blood pressure in laboratory animals, improve the ability to metabolize sugar and have beneficial effects on cholesterol.

Now let's analyze the potential medical benefits of apple cider vinegar. In one interesting study, researchers removed the ovaries of mice to increase their oxidative stress and to mimic menopause; then they fed the mice a high-cholesterol diet. One group of mice was given apple cider vinegar, while another group was not. The mice given apple cider vinegar had improvements in their cholesterol; a decrease in the oxidation of LDL, the so-called "bad" cholesterol; and an increase in the antioxidant glutathione. However, there were only 10 mice in each of the groups, so the numbers don't carry much power.

In a French study of rats fed a high-fat diet and apple cider vinegar, researchers found a decrease in blood sugar and benefits in all cholesterol numbers -- triglycerides, LDL cholesterol and HDL cholesterol. Researchers also found in the apple cider vinegar group a decrease in food intake and a decrease in body weight. The authors proposed that apple cider vinegar had an effect of reducing appetite. Again, the number of rats in the study was small, with only six in the apple cider vinegar group.

Obviously, rodents are not humans, but that said, many studies of humans have shown that vinegar reduces the glycemic response and the glycemic index of sugars and carbohydrates. Vinegar itself may help lower blood sugar, but the mechanism of action is not understood.

Along those lines, a 2004 study looked at 11 patients who had insulin resistance and 10 patients who had Type 2 diabetes. Compared with a placebo, apple cider vinegar improved patients' insulin sensitivity, meaning that it improved insulin's ability to bring sugar out of the bloodstream and into the cells of the body. Also, apple cider vinegar decreased the rise of both sugar and insulin when the subjects were given a bagel and orange juice -- normally insulin- and glucose-spiking foods.

Lastly, in a Swedish study of 12 healthy males given bread both with and without white vinegar, those who consumed the vinegar showed a lowering of blood sugar and insulin. Those who consumed the vinegar also felt full more quickly.

So the benefit of apple cider vinegar may be in vinegar itself, not anything specific to the vinegar from the fermentation of apples. But because the studies above didn't all concern humans and weren't conducted long-term, it's difficult to make a conclusion about the benefits of apple cider vinegar or any other vinegar.

(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.)