Dear Doctor: Can lutein really help prevent, or treat, macular degeneration?

Dear Reader: Age-related macular degeneration, or AMD, is the leading cause of irreversible blindness in the elderly. It's a progressive disease affecting the macula, the central portion of the retina involved with central vision. Changes linked to AMD generally begin after the age of 40, and estimates suggest that approximately 50 million people worldwide suffer from some form of AMD. Further, rates of people with late stages of AMD are increasing.

Research has long suggested that diets high in lutein -- an antioxidant related to beta-carotene and vitamin A -- could reduce the risk of the disease. Like its better-known cousins, lutein is one of nearly 700 organic pigments called carotenoids that absorb light energy and act as antioxidants in plants, bacteria, fungi and algae. A special characteristic of lutein -- and of another carotenoid, zeaxanthin -- is that they accumulate in the retina of the eye and help form retinal macular pigment. This pigment absorbs damaging blue and near-ultraviolet light and thus protects the macula from light injury. In addition, these carotenoids' antioxidant effects help protect the eye from various types of damage.

A typical American diet contains 1 to 2 daily milligrams of lutein. It's found in high amounts in spinach, kale, parsley and romaine lettuce. It is found in lesser amounts in pistachios, asparagus, broccoli, green beans and eggs. One interesting aspect of eggs is that the fat content of eggs allows for better absorption of both lutein and zeaxanthin. Also, cooking oils and oils in salad dressing can increase the absorption of dietary lutein and zeaxanthin.

A 2012 analysis of six studies evaluated whether diets high in lutein and zeaxanthin had any effect on macular degeneration. The participants in the studies were followed from five to 18 years. None of the studies found any impact on the early changes associated with macular degeneration. However, the four studies that assessed impact on more advanced macular degeneration showed a 26 percent reduction among people with the highest dietary intake of lutein and zeaxanthin compared to those with the lowest intake.

The evidence for supplement use is less clear. One study, known as AREDS2, assessed the impact of 10 milligrams of lutein and 2 milligrams of zeaxanthin in supplement form among 4,203 adults over the age of 50 who already had the beginning stages of macular degeneration. After five years, those who took lutein and zeaxanthin had a 10 percent reduction in the rate of advanced AMD. Note that the study didn't include those without macular degeneration.

It's clear that lutein is helpful in the diet, but in regard to the prevention of macular degeneration, there is thus far insufficient evidence that taking a lutein supplement makes a difference for most people.

If you have been diagnosed with AMD or have a genetic susceptibility to the disease, you should certainly boost your dietary intake of lutein and zeaxanthin by increasing the amount of spinach, kale, lettuce and eggs in your diet. You should also exercise regularly and, of course, not smoke.

If you already have the early stages of macular degeneration, you should not only increase your dietary intake, you should consider supplements of both lutein and zeaxanthin.

(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 have read that screening guidelines for prostate cancer are changing again. Why does this keep happening, and why should I believe the latest guidelines if they're just going to be rewritten in a couple of years?

Dear Reader: By its very nature, medicine is an ever-advancing discipline. Findings from new and ongoing research not only push the frontiers of understanding, but they also cast light on what is already known. As a result, the latest information gets incorporated into present-day medical practice. This leads to continual -- and sometimes unsettling -- change.

Let's start with what a screening test actually is.

Unlike diagnostic tests, which are performed to pinpoint the reason for specific symptoms, screening tests are performed in individuals who feel well. Their purpose is to catch a disease or condition in its earliest stage, when it is easiest to treat or manage. Hearing tests, mammograms, pap smears, colonoscopies, blood cholesterol levels, urinalysis, HIV tests -- all are examples of various screening tests performed for different reasons.

You're right when you say that screening recommendations seem to be always changing. The recent history of prostate cancer screening can help explain why.

The PSA test, or prostate-specific antigen test, was once routinely used to screen for early-stage prostate cancer. It's a test that measures the level of a certain protein in a man's blood, which can be an indicator of prostate cancer. But elevated PSA levels may also be the result of benign enlargement of the prostate, or an inflamed prostate due to an infection. It can also be the sign of a very slow-growing cancer. This meant that men with elevated PSA levels often underwent invasive procedures like biopsies even when they did not have prostate cancer, or when their disease was growing so slowly that it would never cause symptoms.

Although some patients were helped by PSA testing, the data showed that many underwent treatment without benefit. This led to new screening guidelines in 2008, and again in 2012. To prevent men from having unnecessary procedures, it was recommended that men within certain age groups rely on active surveillance rather than the PSA test to detect prostate cancer.

Now, though, new data and additional studies suggest the need for a higher level of vigilance. As a result, further changes to prostate screening guidelines are under consideration.

If approved, the new guidelines will recommend that men between the ages of 55 and 69 talk to their physicians about whether a PSA test is appropriate for them. They should also discuss how frequently the test should be performed. Risk factors like age, race, lifestyle, family history, environmental factors and inherited gene mutations will play a part in this shared decision-making process.

Despite the confusion that can result from these changing guidelines, we believe that screening is important. The test results, when put into the context of years, create a valuable timeline. And when done properly and appropriately, the right test at the right time can save your 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: Every now and then, I'll see a news story about the benefits of daily aspirin. A recent story linked it to a lower risk of cancer. What gives? Just how healthy is aspirin?

Dear Reader: We've long known that aspirin can reduce the chances of heart attack and strokes in people at high risk for the conditions. In fact, studies on those benefits provided the first inklings of a decreased risk of cancer, especially colon cancer.

Although those studies themselves couldn't verify the benefit of aspirin, what we know about the drug supports such a connection. Aspirin inhibits cyclooxygenase-2, or COX-2, an enzyme important to the formation of inflammatory compounds. Hypothetically, the loss of these inflammatory compounds, called prostaglandins, may lead to decreased cellular replication and decreased recruitment of new blood vessels. That is, with a reduced ability to multiply and grow, cancer cells could have less of a chance to take hold.

One of the earliest assessments of aspirin's impact on cancer came from the Women's Health Study, which randomized 39,876 women to taking a placebo or 100 milligrams of aspirin every other day. The women were followed on average for 10 years, and the majority had additional follow up for 7 1/2 additional years. Researchers found little difference in the rates of breast, lung and many other cancers, but after 10 years, they found a 20 percent reduction in the rate of colon cancer among those taking aspirin. The decrease of colon cancer was even greater among women who continued taking aspirin in the 7 1/2-year follow-up period. Note that there was a 14 percent increase in incidents of gastrointestinal bleeding among those taking aspirin versus placebo, but no change in death rates from bleeding between the two groups.

A 2016 study assessed aspirin use among patients in two large ongoing studies: the Nurses' Health Study and the Health Professionals Follow-Up Study. The combined studies looked at 88,084 women and 47,881 men who had been followed since the 1980s. Those who used aspirin two or more times per week, in either regular or "baby aspirin" doses, had a 19 percent reduction in colon cancer and a 15 percent reduction in stomach and esophageal cancers. However, this benefit was not noted for any other cancer.

Further, the decrease in colon cancer rates became significant only after five years of taking aspirin. The authors note that the population in these two studies was predominantly Caucasian and so may not be applicable to other races.

The same researchers recently presented a follow-up to this study to the American Association for Cancer Research. In this re-evaluation, the authors found a 31 percent decrease in the risk of colorectal cancers -- as well as reductions in breast, prostate and lung cancers. The reasons for such significant improvements are unclear.

Overall, the data point to a 20 percent reduction in colorectal cancer risk with the regular use of aspirin -- specifically 81 milligrams every other day -- but the numbers for other cancers are not convincing.

Be aware, however, of the risk of gastrointestinal bleeding. If you've had an ulcer or stomach problems with aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDS) in the past, daily aspirin use is not for you.

(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.)