Dear Doctor: Should I take large doses of vitamin D to prevent osteoporosis?

Dear Reader: This is an excellent question. Vitamin D appears to be a wonder vitamin in regard to health. For whatever ails you, it seems, vitamin D is the cure. But that's not necessarily true.

Vitamin D is so crucial for healthy bones that deficiencies in children lead to the malformed bones seen in rickets. Because vitamin D helps the body absorb calcium, it's vital for a host of other biological functions as well. In fact, vitamin D acts more like a hormone in that way.

The recommended daily allowance of vitamin D is 600 to 800 units. It can be found in foods fortified with vitamin D -- and the numbers of those products seem to be increasing -- or from fatty fish or eggs. But the majority of the vitamin D that our bodies need begins with UVB light; our bodies use this light to produce the precursors of vitamin D.

Adults who are out in the sun regularly and have normal vitamin D levels probably don't need a vitamin D supplement. A meta-analysis published in the renowned medical journal The Lancet reviewed 24 studies that followed patients who took vitamin D. The research found little change in bone density with supplementation of vitamin D. Some studies found that vitamin D reduced the risk of bone fracture -- but only when it was combined with calcium.

Calcium on its own has been shown repeatedly to decrease the risk of fractures. Vitamin D on its own has not been shown to decrease fracture risk.

Some practitioners recommend mega-doses of vitamin D to their patients, causing very high blood levels of it. But high levels of vitamin D in the bloodstream might actually increase the rate of bone breakdown.

The highest daily intake considered safe by the Institute for Medicine is 4,000 units. If you are taking vitamin D, have your blood levels checked. For the prevention of osteoporosis, the Institute of Medicine recommends a vitamin D blood level greater than 20 ng/mL (nanograms per milliliter). The majority of people can achieve this level without supplementation, but if you do supplement, 600 units is more than sufficient.

As for all the other purported health benefits of vitamin D, such as its ability to decrease the risk of cancer and heart attacks, there may be benefit to vitamin D intake, but we're not sure yet. We need good long-term studies that compare people who take vitamin D daily against those who don't.

Until then, if you don't have osteoporosis and you do have sufficient vitamin D levels in your blood, there appears to be little additional benefit to taking a vitamin D supplement.

(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: I love to go for long walks and lately have noticed that I'm developing pain in my hip joints. I think that's just part of aging, but my daughter is urging me to try a glucosamine supplement. Can this really be helpful?

Dear Reader: Glucosamine is a compound that is naturally produced within your body. It plays a key role in building and maintaining healthy cartilage, the connective tissue between your joints. Tough and flexible, cartilage provides a smooth, lubricated surface over which bones can easily move and glide without friction or pain.

But cartilage has a limited ability to repair itself. When it is damaged, or when it wears away over time as we age, the resulting joint pain and stiffness can turn even the simplest tasks into an ordeal. Loss of cartilage, which leads to degeneration of the underlying bone, is what makes osteoarthritis so painful.

The use of glucosamine, a supplement sold in capsule and tablet form, became popular in the 1990s after several best-selling books touted it as a hedge against osteoarthritis. Several studies had suggested that glucosamine has anti-inflammatory properties and might even aid in the regeneration of cartilage. Sales of the dietary supplement spiked.

However, subsequent research has offered conflicting medical data about the benefits of glucosamine. In the largest study thus far, which looked at more than 1,500 adults with osteoarthritis of the knee, glucosamine proved to be no more effective than a placebo. Only the participants who were given acetaminophen for pain reported ongoing relief.

In several other studies, meanwhile, participants with osteoarthritis of the knee and hip who took glucosamine reported reduced pain and swelling, as well as increased range of motion. Little wonder that the glucosamine debate is lively and occasionally contentious.

If you do decide to give glucosamine a try, the National Institutes of Health report that glucosamine appears to be safe and well tolerated when taken in suggested doses over a two-year period of time. Although infrequent, reported side effects are headache, indigestion, heartburn and constipation. Since glucosamine is made from shellfish, including shrimp and crab, individuals with shellfish allergies or who are sensitive to iodine are warned to avoid it.

It's also an excellent idea to also follow recommendations put forth by the American College of Rheumatology. Their panel of experts -- primary care physicians, rheumatologists, geriatricians, surgeons, physical therapists and other health care professionals -- suggests the following:

-- Exercise: Thanks to increased muscle strength and toning, individuals with arthritis who exercise regularly have more energy, report less pain, sleep better and are better able to carry out daily tasks.

-- Lose weight: Every extra pound that you carry puts additional stress on your knees, hips and spine.

-- Medication: Check with your primary care physician whether oral or topical pain relievers might be helpful. Acetaminophen is a common first treatment for osteoarthritis. Nonsteroidal anti-inflammatory drugs, also known as NSAIDs, can also help with pain and swelling.

As with any treatment plan, make your primary care physician your partner. Whether it's giving your daughter's idea about glucosamine a try, or following through with the American College of Rheumatology's recommendations, your doctor is there to help, encourage and guide you.

(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.)

(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: Does my cholesterol medication increase my risk of cancer?

Dear Reader: I assume you're asking about statins, the most commonly prescribed type of cholesterol-lowering medication. These drugs, which work by lowering cholesterol levels in the bloodstream, are generally regarded as both safe and effective. They're so effective that widespread statin use, along with a decline in smoking rates and an increase in the use of cardiac stents, have helped decrease the U.S. death rate from heart attacks.

However, some research has suggested that long-term statin use may have unintended negative effects, including an increase in the risk of cancer. This potential connection originated in now-dated studies showing that lower levels of LDL, the so-called "bad" cholesterol, were associated with an increased risk of cancer. The problem with this line of reasoning is that people with lower LDL may have more underlying illnesses that can also increase their risk of cancer. Many older studies did not take that connection into account.

Furthermore, other studies suggesting a link between statins and increased cancer risk looked only at total cholesterol, which also includes HDL, the so-called "good" cholesterol. Lower levels of good cholesterol aren't affected by statins and could be a separate risk factor for disease. Take, for example, the case of smokers. They generally have lower levels of HDL cholesterol, so their total cholesterol may be lower as well. In short, a lower total cholesterol number could be a red herring when assessing cancer risk.

It's true that observational studies have shown increased cancer rates among patients taking statins, but these studies were small and not well-controlled. More well-controlled studies point to the possibility of a slight decrease in cancers among people who take statins. One study, published in the New England Journal of Medicine, analyzed data on more than 60,000 people who used statins and found a 15 percent decrease in cancer death rates compared to those who had never used statins.

In fact, many studies are now assessing the potential of statins to be used in therapy against certain types of cancers.

I have had many patients fearful of statins for a variety of reasons, such as worry about muscle pain or a potential increased risk of diabetes or cancer. Their worry may stem in part from a fear of taking a medication every day to prevent problems that don't currently exist.

That's understandable, especially when the patients currently feel healthy. But the fact remains: Statins decrease the risk of heart attacks and don't appear to increase cancer rates. In summation, if you need a statin, you should take it.