Dear Doctor: My 83-year-old mother has advanced osteoporosis. She and I recently read several articles touting the benefits of vitamin K2. Does it help strengthen bones? If so, what is the recommended daily dose? Are there side effects?

Dear Reader: Vitamin K is necessary for the coagulation of blood. There are two main forms, appropriately named vitamin K1 (phylloquinone) and K2 (menaquinone). The major source of K1 is green vegetables, while K2 is produced by the bacteria in the intestine. K2 also can be obtained from fermented soy, cheese and curds.

Vitamin K helps the hormone osteocalcin create more structurally sound bone in a process called carboxylation. When vitamin K levels are low, the carboxylate form of osteocalcin is also low, leading to more fragile bone. Vitamin K also increases the activity of cells involved in bone formation and decreases the activity of cells involved in bone destruction.

Low vitamin K consumption and decreased blood levels of vitamin K are each associated with an increased risk of hip fractures in men and women, so one could assume that taking supplements would naturally help decrease the rate of hip fractures. The evidence, however, isn't completely convincing.

A 2006 analysis of seven Japanese studies looked at the K2 supplement menaquinone-4. Six of the trials assessed the impact of 45 milligrams of menaquinone-4 in women over the age of 55. The trials lasted 12 to 24 months. The supplement led to a decrease in overall hip fractures by 6 percent, spinal fractures by 13 percent and all other fractures by 9 percent. The authors also showed improvement in bone density with the use of either vitamin K1 or K2.

A 2015 combined analysis of 19 randomized controlled trials similarly analyzed the impact of K2 supplements. Ten of the studies focused on people with osteoporosis, and the researchers found, as expected, an increase in the carboxylate form of osteocalcin among those taking K2. In women without osteoporosis, there was no difference in bone density among those who took K2. Women with osteoporosis showed an improvement of spinal bone density, but no change in hip bone density. (Note that, although this was a combined analysis, two-thirds of the patients came from one study in Japan.) Lastly, a 2016 Japanese study found improvement in bone density when vitamin K2 was combined with a bisphosphonate medication.

Few studies outside of Japan have assessed the impact of K2 supplements, so it's difficult to say whether supplementation might have the same impact for Americans. The typical Japanese diet is very different from the typical American diet, so factors other than K supplementation may play a role in fracture risk and bone density -- or vitamin K may be more necessary in a Japanese diet.

A 2009 study in the United States enrolled 381 postmenopausal women with low bone density to take either vitamin K1 (1 milligram), vitamin K2 (menaquinone-4 at 45 milligrams) or a placebo for 1 year. The authors found no difference in bone density or bone markers between the three groups, except that the carboxylate osteocalcin was higher in the groups that took either form of vitamin K.

That said, vitamin K2 supplements have been linked to greater amounts of nausea and abdominal pain compared with placebo. Of special note, vitamin K should not be taken with the blood thinner warfarin because it counters the effect of the drug.

Although the devastating impact of hip fractures underscores the need for improved bone-strengthening options, we need randomized trials in the U.S. and Europe evaluating K2 supplements before we can make broader conclusions about their benefit.

(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: Whenever I offer a certain friend a ride, she kindly declines, explaining that, because I have Type 1 diabetes, she's afraid my blood sugar will suddenly crash and I'll get into an accident. I know it's just ignorance and try not to be insulted. Can you help explain why most people with diabetes are OK to drive?

Dear Reader: It's true that people living with Type 1 diabetes run the risk of hypoglycemia, which is when blood sugar becomes dangerously low. This can lead to physical reactions that would make driving dangerous.

The early warning signs of hypoglycemia include shakiness, dizziness, hunger, mood swings, headache, sweating and anxiety. If left untreated, hypoglycemia can lead to blurred vision and slurred speech, jerky or uncontrolled movements, confusion or muscle weakness. At its most extreme, it can cause seizures or convulsions and result in death.

However, when diabetes is properly managed, serious episodes of hypoglycemia tend to be infrequent. The majority of people with Type 1 diabetes who adhere to specific safe-driving guidelines drive regularly without medically related incidents. By remaining vigilant about blood glucose monitoring and being prepared for a quick correction by eating a fast-acting sugar snack, most people with diabetes can successfully manage an episode of hypoglycemia.

We agree that your friend's fears stem from a lack of knowledge about diabetes. Perhaps learning about the precautions set out by the American Diabetes Association, with an eye to helping people with diabetes live full and safe lives, will give your friend some peace of mind?

-- Before you set out on a drive, check your blood glucose. On longer trips, it's important to stop and do periodic checks to be sure you're in the optimal range.

-- Make it a habit to stock the car with a special driving kit. Include your blood glucose meter and lots of snacks, including several that are quick-acting sources of sugar. Hard candy, fruit juice or glucose tablets will do the trick.

-- Are you feeling any of the signs of hypoglycemia during your drive? Pull over immediately (seriously, immediately, because things can go wrong so quickly), and check your blood glucose level.

-- Is your blood glucose low? That's the time for one of those fast-acting sugar sources. Take a 15-minute break and do another check. If you're in the zone, it's OK to start driving again.

-- It's very important to stay current on eye exams, so you can catch any diabetes-related vision problems as quickly as possible.

There is one very important caveat.

If you have experienced an episode of hypoglycemia unawareness, which is when you are unable to detect the warning signs that your blood glucose is low, you must give up driving until awareness has been re-established. This is for your own safety, and for those around you. Call your doctor to talk about treatment strategies.

So ask yourself: Is your diabetes under control? Are you able to quickly detect and promptly respond to an episode of hypoglycemia? Will you follow the ADA's driving guidelines? If so, you can reassure your friend about your ability to take the wheel.

(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 doctor at the local bone and joint clinic said I was a good candidate for an experimental injection of PRP for arthritis in my right shoulder. What is your opinion? I'm 71.

Dear Reader: Unlike your doctor, I'm not familiar with your medical history or your shoulder condition, so I can't offer a specific medical opinion. What I can do is explain a bit more about this procedure and its potential.

First, some background: Because tendons, ligaments and cartilage have limited blood flow, the body's ability to repair them is limited. Autologous platelet-rich plasma (PRP) aims to compensate for this. It's prepared by removing about 30 to 60 cubic centimeters of blood from your arm. The blood is then filtered through a process called plasmapheresis, which concentrates the platelets. The wonderful thing about platelets is that they're usually the first blood component to arrive at the site of an injury, bringing molecules that encourage healing. Thus, platelet injections have the potential to improve healing of an area with normally poor blood flow.

Most studies of PRP for the shoulder have involved people having surgical repair of the joint, with surgeons using PRP to bolster a rotator cuff repair or to boost healing after shoulder replacement. A 2015 study combined data from eight studies comparing arthroscopic surgery for rotator cuff tendon tears with PRP and without PRP. Of 464 patients, 234 had PRP injections. The authors found no difference in the rates of tendons re-tearing after surgery, nor did they find any significant MRI changes in the PRP group. Further, the studies did not find any difference in range of motion or pain with the use of PRP.

Another 2015 analysis -- this one of 11 studies with a total of 597 patients -- also failed to show MRI or symptom benefit with the use of PRP. However, PRP did show benefit among people who had rotator cuff tendon tears greater than 3 centimeters. A 2016 study showed benefit in the use of PRP in the first month after surgery, but no significant benefit after six months.

Also, there are small studies that show PRP can help people who are not having shoulder surgery. Some studies have compared PRP to steroid injections in the shoulder for partial rotator cuff tears or for impingement syndrome and found that PRP was equivalent or even more helpful than steroid injections. However, a study from Iran found that while PRP did ease pain and improve mobility of the shoulder, it was not superior to physical therapy.

As for arthritis of the shoulder, I haven't found good studies to support the use of PRP. Some studies show benefit for arthritis of the knees, but their poor design and lack of comparison subjects make conclusions difficult.

That said, while I don't know the degree of your shoulder arthritis, if you have impingement of the shoulder or a partial tear of your rotator cuff tendon, PRP in addition to physical therapy may have benefit.

I'm with your doctor on this: It's worth a try.

(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.)