Dear Doctor: I have heard recently from a friend that watching internet pornography can lead to erectile dysfunction. Is this true?

Dear Reader: Your friend may not be far from the truth. To put it simply, the rates of erectile dysfunction have significantly increased over the last 15 years. This has especially been noted in men younger than 40. In 2002, a review of 23 studies from Europe, the United States, Asia and Australia found that the rate of erectile dysfunction in that age group was 2 percent. But in 2011, a study of Europeans found that the rate of erectile dysfunction in men ages 18 to 40 ranged from 14-28 percent. Further, a 2014 study of 367 military personnel ages 21 to 40 found erectile dysfunction in 33.2 percent of the men. Even when excluding military personnel with post-traumatic stress disorder, the rate of erectile dysfunction was 15.7 percent.

Older men can have many physiologic causes for erectile dysfunction, but these are much rarer in younger men. Among such causes are vascular disease from years of smoking, high blood pressure and diabetes. Further, while rates of obesity and diabetes have increased among those under 40, the rate of cigarette smoking has decreased. So, if the risk factors for ED have not increased substantially, why the dramatic risk in ED? Some have said that the increase in erectile dysfunction has coincided with easy access to internet pornography.

In fact, many studies have found a correlation between an increase in pornography use and a decline in sexual desire, sexual arousal, enjoyment of sexual intimacy and sexual satisfaction as well as more sexual problems, such as erectile dysfunction. Addiction to pornography seems to affect the brain reward pathways, leading to a reward mechanism that can only be fulfilled with cues found in pornography and dulling the brain's responsiveness to normal sexual stimuli. In a way, increasing pornography desensitizes the individual to sexual stimuli.

However, two studies contradict the idea that internet pornography leads to greater erectile dysfunction. The first -- a study of 280 men -- found a correlation between a weekly increase in the watching of sexual stimuli and a mild increase in the desire for sex. The second -- an online European study of 2,737 men under the age of 40 -- found no link between the use of pornography and sexual dysfunction, though it did find higher rates of low sexual desire than had been reported in past studies of this age group.

Ultimately, pornography may not be the underlying issue. For one, more men may be using pornography because of a greater feeling of isolation and a greater inability to be sexually intimate. Second, a society that spends much of its time on computers, both in work and personal time, fosters a decrease in -- and alteration of -- human contact, which may lead to anxiety with sexual intimacy.

The fact remains that the rates of erectile dysfunction are increasing in men younger than 40, and while pornography may be part of the equation, it may actually be a symptom and not a cause. The bigger issue may be greater social isolation and difficulties with intimacy.

(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: Just how unsafe is chromium-6, the chemical at the heart of the movie "Erin Brockovich"? I read that it's still in the water in some parts of the country. How is that possible? How do I find out about water quality in my area?

Dear Reader: While the characters and events in "Erin Brockovich" may have been embellished to serve the dramatic arc of the story, chromium-6, when present beyond certain concentrations, is as toxic as the film portrayed. Breathed in, it can cause lung cancer. Ingested, it has been linked to liver and kidney damage, serious reproductive problems, rashes and skin conditions, and developmental harm to infants and children.

Chromium is a metallic element that occurs naturally in soil, rocks, plants and volcanic dust. It is found in several forms, including chromium-3, an essential micronutrient that plays a role in the breakdown of fats, proteins and carbohydrates. Chromium-6, by contrast, is a toxic form of the element. Also known as hexavalent chromium, it's a byproduct of the natural chemical breakdown of chromium and is created in greater quantities through various industrial processes.

Both forms of chromium are used in applications such as chrome plating, making pigments and dyes, the manufacture of stainless steel, preserving wood and leather products, and, as depicted in "Erin Brockovich," in the treatment of water in cooling towers. Exposure to large amounts of any kind of chromium, which has numerous uses in manufacturing, has been known to cause respiratory problems like shortness of breath, wheezing, cough and even asthma.

When industrial users of chromium-6 fail to take proper precautions when they store or dispose of the chemical, leakage and runoff from the manufacturing process can pollute the groundwater. And while the EPA has set a limit on what it refers to as "total chromium," the sum of chromium-3 and the far more toxic chromium-6, at this time it has not set a limit solely for chromium-6. California, home to the landmark chromium-6 lawsuit at the heart of "Erin Brockovich," has placed a legal limit on chromium-6 concentrations in the water, but some activists believe the allowable levels remain too high.

You've posed an important question when you ask about how chromium-6 continues to enter our drinking water supply. But the answer is complex. Providing potable drinking water to a nation as vast and populous as the United States remains an ongoing challenge. Since the establishment of the Clean Water Act in 1972, health and safety standards have been set at the federal level. However, water is a regional resource. That means oversight of the tens of thousands of state, local and private water utilities that make sure our taps are flowing falls to a complex patchwork of regulatory agencies. As a result, water quality can vary greatly depending on where you live.

If you live in a community whose water system serves more than 100,000 people, it is required to post reports on water quality online. If you live in a smaller community, check with your local government agency to learn where and how to find reports regarding your specific provider. For more information, go to water.epa.gov/drink/index.cfm.

(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 a middle-aged woman on blood pressure medication, but recently heard that one type of this medication could raise the risk of pancreatic cancer. What type is that, and if it's mine, should I change?

Dear Reader: It's scary to think that a medication to improve your health could also cause disease. So let's take a closer look at the recent data from the Women's Health Initiative on the possible link between blood pressure medications and pancreatic cancer.

In the study, 145,551 postmenopausal women, ages 50 to 79, were asked about their use of anti-hypertensive medications. The women were followed on average for about 13.8 years, and 841 cases of pancreatic cancer were noted in that time. Women who had ever used calcium channel blockers (CCBs) for high blood pressure had a 33 percent increased risk of the cancer compared to those who had never used the drugs. Those who had used the drugs for three years or more had a 48 percent increased risk of pancreatic cancer compared to those who never used them.

Calcium channel blockers have been around for many years, with most of those used in the past being the short-acting variety. The authors found that women who had ever used the short-acting type had a 66 percent increased risk of pancreatic cancer, and those who had used them for three or more years had a 107 percent increased risk -- both as compared to women who had never used the drugs.

Keep in mind that most CCBs given today are the extended-release variety. When the authors looked at the extended-release CCBs, they found no association with pancreatic cancer. Nor did they find an association with any other medication for high blood pressure. At the time of this writing, the full article about the findings was not yet available, so it is difficult to know if confounding factors were involved, but the authors did say that they adjusted for obesity, diabetes, smoking and age.

The traditional short-acting CCBs are verapamil, diltiazem and nifedipine. As for why they might increase the risk of pancreatic cancer, chronic inflammation may play a role. The authors theorized that CCBs may block the release of a receptor needed to counter inflammation. In fact, in the 489 pancreatic cancer patients in whom levels of the receptor were measured, CCBs reduced the level of the receptor, thereby theoretically increasing the rate of pancreatic cancer.

While the preliminary data are concerning, they're not wholly definitive. If you're taking the short-acting verapamil, diltiazem or nifedipine, I would consider switching to an extended-release form of this medication. Although long-acting CCBs have not been associated with risk, you could also consider changing to an entirely different class of medication, such as an ACE inhibitor, an angiotensin receptor blocker, an alpha blocker, a diuretic or a beta blocker. Your doctor is the best person to decide which is the most appropriate choice.

And please note: The data was taken from postmenopausal women, so it may not be applicable to women who have not gone through menopause or to men.

(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.)