Dear Doctor: I have Type 1 diabetes and have used marijuana for years to control my blood sugar. I've seen my blood sugar drop 100 points in five minutes with marijuana, a lot faster than my Humalog insulin can manage. Why is that? Will medical marijuana ever go mainstream?

Dear Reader: Marijuana, or cannabis, contains more than 100 active chemical compounds. Known as cannabinoids, each of them behaves differently in the body. As the number of states that allow the use of cannabis for medical purposes continues to grow, so does the body of evidence that many of the compounds found within the plant have therapeutic potential. The most common use of cannabis in the United States right now is for pain control. It's also widely used for anxiety, to manage nausea and has been shown to be effective in reducing inflammation. It also shows promise in managing symptoms of neurological conditions like Parkinson's disease and multiple sclerosis.

The challenge to investigating medical claims regarding cannabis is the fact that, despite what's happening in individual states, it remains illegal at the federal level. Cannabis is a Schedule l drug, in the same category as heroin, which means research is subject to numerous restrictions. Even so, various studies and clinical trials are moving forward, and in time we will learn more about what cannabis can -- and can't -- do.

In researching your question regarding cannabis and diabetes, we found that you're not alone in noticing its effect on blood sugar. However, much of what we found is anecdotal evidence, which lacks scientific rigor. At this time, the study of cannabis and its potential effects on diabetes is in the early stages, with much of the work done in mice and on donated tissue samples. Until researchers are able to work extensively with human populations, the how and why of the effects of cannabis on the complex physiologic processes encompassed by diabetes will remain educated guesses.

Preliminary research suggests that certain cannabinoids may help with glucose control. Some studies have found that cannabis can have a positive effect on insulin resistance. A study published in 2016 in a journal of the American Diabetes Association found that THCV, one of the cannabinoids that are not psychoactive, improved glycemic control in some individuals with Type 2 diabetes. Another study that same year drew a link between cannabidiol, a compound in cannabis, and a decrease in inflammation of the pancreas. In an observational study using data from the federal Centers for Disease Control and Prevention, researchers found the incidence of diabetes among regular cannabis users to be measurably lower than that of the population at large. At the same time, the results of several other recent studies contradict a number of these pro-cannabis findings. So, basically, the jury is still out.

Although cannabis shows promise in the area of diabetes, science has yet to catch up with the claims being made. In the research that has been done, the reason for the effects of cannabis are not yet fully understood. Interest in the subject is strong, though, and continues to grow. We'll keep an eye on the topic for you and report back as we learn of new advances.

(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 daughter isn't a flight attendant, but she flies a lot for business. Is she at an increased risk for cancer?

Dear Reader: Commercial airline flying is a relatively new experience. The concept of flying to multiple locations for business would have been inconceivable 100 years ago. The evolution of the human body has not been adapted to flight, so the exposure of humans to prolonged airplane travel is a change that may have health consequences. At higher altitude there is greater exposure to ionizing radiation. Flight attendants and pilots spend much of their working time 30,000 feet above the Earth's surface, so their health may give us an indication of potential hazards with flying.

A recent study in the journal Environmental Health looked at 5,366 former and current flight attendants and compared them with a control group of the same age and health. More than 80 percent of the flight attendants were women. The average age of the participants was 52 and the average duration at the job was 20 years.

The authors looked at the number of cancers in the flight attendants and found a greater rate of cancer overall compared with the control group. In women, there was a 51 percent greater prevalence in breast cancer, a 2.27 times greater risk of melanoma and a 4.09 times greater risk of other types of skin cancer. The elevations of skin cancer were not as great among male flight attendants. There were also increases in the rates of uterine, cervical, gastrointestinal and thyroid cancer among female flight attendants.

The rate of cancer increased with every five-year increment in the air for non-melanoma skin cancers, but this was not noted with other types of cancer. This result is confusing because one would believe there would be greater numbers of cancers based on greater flight time. What is also confounding is that the flight attendant group had fewer children on average than the control group, which should lower the rate of breast cancer in the control group compared to the flight attendants (the greater number of children a woman has incrementally lowers the rate of breast cancer). The authors, though, still found a modest increased rate of breast cancer in flight attendants with the same number of children as the control group. Lastly, the study doesn't take into account the amount of time flight attendants spent on layovers and vacations in the sunshine. This would appear to be greater than the control group and could be a reason for the increased rate of skin cancer.

Nonetheless, ionizing radiation is a risk factor for breast and non-melanoma skin cancers. Cabin crews have the highest annual ionizing radiation dose out of all American workers. While I believe there is a greater risk of cancer among flight attendants, I also feel that confounding factors may make the risk less than what is reported.

But this doesn't really answer the question regarding your daughter. Flight attendants have a substantially greater number of hours in the air than your typical business commuter. Thus, I feel your daughter may not be at a significant risk of cancer from her relatively short time in the air. But I would feel even more comfortable saying this if there were some way to protect both passengers and cabin crews from ionizing radiation.

(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 always reach for the highest SPF when I'm buying sunscreen, especially for the kids. But my mom says what matters most is the type of UV rays the sunscreen is blocking. Why is that? What does SPF actually measure?

Dear Reader: There's a lot of confusion when it comes to sunscreen. We've had patients admit that when they get overwhelmed by the labels and the choices while shopping for sunscreen, they sometimes give up and decide to go without. But sunscreen can help prevent skin cancer. In fact, it is estimated that exposure to the sun's UV rays is responsible for up to 90 percent of non-melanoma skin cancers and at least 65 percent of melanomas. And while it's not quite in the same life-or-death category, UV rays are also responsible for signs of premature aging like wrinkles, brown spots and sagging skin.

Let's start with the basics. Sunlight is the portion of the sun's radiation that reaches us at the Earth's surface. It's made up of three basic components -- the visible light that we see, infrared rays, which deliver heat, and ultraviolet rays. Although we neither see nor feel ultraviolet radiation, it still manages to make its presence known. On the plus side, it triggers our bodies to manufacture vitamin D, an essential micronutrient. But prolonged exposure to the sun's ultraviolet spectrum results in skin damage.

The longer wavelengths of ultraviolet light, known as UVA, are the so-called tanning rays and are known to age the skin. UVB rays, which cause sunburn, play a major role in skin cancer. Although you may hear the axiom regarding UV rays that A is for aging and B is for burn, the most recent research suggests that both types of UV rays play a role in each process. All of which brings us to your question about SPF factors and sunscreen.

SPF stands for sun protection factor. While the ascending numbers of the SPF scale seem to imply an increasing strength or concentration of the sunscreen product, what they actually represent is the length of time that you can spend in the sun before starting to burn. Let's say it takes five minutes in the sun without protection before your skin begins to redden. A sunscreen with an SPF of 10 means that when you apply it, you will have 10 times that amount of time -- 50 minutes -- before you begin to burn. A lotion with an SPF of 30 gives you 150 minutes. Bottom line -- the "factor" in SPF is the number by which you multiply your minutes-to-a-burn time.

By using sunscreen, you've applied a chemical barrier that helps keep UV radiation from reaching the skin. The trick here is to be sure you use a full-spectrum (sometimes known as a broad-spectrum) sunscreen. This means the product blocks both the UVA and UVB rays, which is essential for the best protection. And while this seems like a no-brainer, you really do need to follow the instructions on the product in order to get full protection. Apply at least 15 minutes before heading outside, use at least an ounce or two for adequate coverage, and reapply at least every two hours.

(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.)