Dear Doctor: I had my thyroid removed because of papillary cancer, and my surgeon has advised me to take high levels of vitamin D. He says there may be a correlation between low vitamin D levels and the development of cancer and Alzheimer's disease. If I remember correctly, the normal blood range for vitamin D is between 30 and 60 nanograms per millileter. I take 8,000 units a day, which keeps my blood level near 60 ng/ml. What's the evidence for higher levels of vitamin D?

Dear Reader: You and I share the same past cancer diagnosis -- and the same search for answers. When I was 26, I was also diagnosed with papillary thyroid cancer. At the time, I racked my brain for why I developed this cancer. I was healthy at the time, had a good diet and exercised regularly. I was also outdoors a lot, so my vitamin D levels were good.

As with so many cancer diagnoses, I ultimately couldn't find any factor that would have increased my risk. True, there is a definite link between papillary thyroid cancer and radiation exposure, which can come from radiation fallout due to nuclear accidents, as well as excessive X-ray radiation to the neck and oral area. But I hadn't been exposed to nuclear fallout, and I'd had only the normally recommended dental X-rays. (Today's more modern X-rays expose patients to lower doses than previous generations.)

I haven't stopped looking for connections, however, between a diagnosis of disease, risk factors and possible preventive measures.

That brings us to your current question. The normal blood level for vitamin D is between 20 and 50 ng/ml. This level -- generally considered necessary for good bone health -- is recommended by the Institute of Medicine, which conducted a review of studies on the topic. Some organizations, such as the National Osteoporosis Foundation, recommend 30 to 50 ng/ml as the normal range. But both of these recommendations are about good bone health, not the prevention of cancer and Alzheimer's disease.

The World Health Organization looked at multiple retrospective studies evaluating a potential connection between vitamin D levels and colon cancer. They did find a link between low vitamin D levels and colon cancer, specifically that people with blood levels of 20 ng/ml or less had significantly higher colon cancer rates.

However, retrospective studies look at disease after the disease has happened, and it can be difficult to make a solid correlation that way. A prospective study assessing vitamin D concentrations prior to the diagnosis of colon cancer did not find any evidence that vitamin D levels had any relation to colon cancer.

Studies focused on prostate cancer have shown both benefit and increased risk among people with higher levels of vitamin D, so it would seem that supplementation does not appear to have an impact one way or another. With regard to breast cancer after menopause, an analysis of nine prospective studies showed a decrease in breast cancer rates among women with higher levels of vitamin D, but this decrease was not seen in women whose levels were above 35 ng/ml. Still another analysis of 18 studies assessing overall breast cancer risk in women did not find any benefit to vitamin D supplementation.

In summation, there may be slight benefit to minimal supplementation in women after menopause to get their levels to 35 ng/ml to decrease the incidence of breast cancer. But in men, the benefit of reduced cancer risk has not been shown.

In relation to cognitive decline, a study published in the journal Neurology in 2012 showed a slight increase in Alzheimer's disease in people whose vitamin D levels were lower than 20 ng/ml. The authors concluded that more studies are needed to evaluate the potential connection.

Let's say that there is a benefit to vitamin D supplementation in lowering the risk of cancer and Alzheimer's disease. To reach a level of 20 ng/ml, you probably would not need to take more than 400 units of vitamin D per day. For a postmenopausal woman to reach the benefit needed for a possible reduction in the risk of breast cancer, she probably would not need to supplement with any more than 800 units per day.

In light of the evidence, 8,000 units of vitamin D daily seems too high. The blood serum level of 60 ng/ml also may be too high. Although the topic needs to be studied more, higher amounts of vitamin D could potentially lead to greater bone turnover and possibly weaker bones.

Ask your doctor if you can reduce the amount of vitamin D that you are taking, as there currently is no evidence to support it.

(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've read about a recent study that found that elderly patients with female doctors fared better than those who were treated by men. I wonder -- what do Dr. Ko and Dr. Glazier think about these results?

Dear Reader: You're referring to the results of a study performed by Harvard researchers, published in December 2016 in the journal JAMA Internal Medicine. To say that it caused a bit of a stir is an understatement. Our colleague Dr. Ashley gave his take on these findings yesterday. Our reactions follow later.

Researchers analyzed data from more than 1.5 million Medicare patients 65 and older who were hospitalized between January 2011 and December 2014. What they found was that patients whose doctors were women were less likely to be readmitted to the hospital in the next 30 days, and had lower mortality rates than the patients who were treated by men.

This particular study didn't look into the reasons why, but the authors cited prior studies that found differences in how women and men practice medicine. Specifically, the research suggests that female doctors are more likely to adhere to clinical guidelines, provide more preventive care and communicate more effectively than their male peers.

The Harvard study was prompted, in part, by the fact that women doctors now account for one-third of all physicians and one-half of medical students. Researchers were interested to learn whether career interruptions to start a family, the challenges of home-life balance, and the resulting increase in part-time employment might compromise the quality of care.

So what did we think of the results?

Dr. Glazier: My gut reaction is that it is very hard to generalize. As a patient, I have had both men and women who were extraordinary and compassionate physicians. And I have had teachers, mentors and colleagues who are exceptional, irrespective of their gender.

Considering that this is a single study of modest statistical significance, I don't give it tons of credence. What I would say is that it is paramount to find a doctor with whom you connect both personally and professionally, someone who is compassionate, kind and smart, all qualities that transcend gender.

Dr. Ko: As a female physician early in my career, I am naturally delighted to hear the findings. Medicine has historically been dominated by men, who have been seen as more intelligent and more capable than women. The results are validating and confirm my role to perform this noble work.

The authors admit they can't answer the question "Why?" But since prior studies suggest that women tend to communicate better, listen more effectively and have more emotional intelligence, then the message here is that communication is key. Our training of young physicians should focus on honing these skills and exemplifying these qualities.

The danger is that some patients may oversimplify these results, assuming that to prevent death and re-hospitalization, they need a female physician. But the truth is that there are as many male physicians who are compassionate communicators as there are women physicians who lack those qualities.

What I do hope is that all physicians will take a cue from these results to embrace the qualities and behaviors that may contribute to better care.

(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: Do hospitalized patients really get better care from female doctors compared to men, as a new study -- and now many headlines -- claim?

Dear Reader: My initial reaction when I saw this study was one of denial. As a man, I viewed the study -- and the host of media articles reporting on it -- with something like hostility; it seemed no less than an attack on my gender. After I calmed down a bit, I read through the research.

The study, published recently in JAMA Internal Medicine, looked at a random sample of data -- totaling more than 1.5 million hospitalizations -- from four years of hospitalizations among Medicare patients being cared for by general internists. The authors separated the patients into two groups based on the gender of their physicians, then evaluated quality of care by the death rates of these patients within a 30-day period after hospitalization and also by the rates of readmission to the hospital after being discharged.

The authors found that the death rates of patients cared for by female internists were slightly lower than the death rates of patients cared for by male internists: 11.07 percent versus 11.49 percent. This was not a staggering difference -- amounting to one fewer death in 233 patients -- but still, it was a difference. Further, readmission rates were lower for patients of female doctors compared to patients of male doctors: 15.02 percent versus 15.57. This means one fewer readmission in 182 patients.

Even as a man playing devil's advocate, I can't blame confounding factors -- differences in patient characteristics -- for the findings. Female doctors took care of more female patients, slightly fewer patients with heart disease, lung disease and diabetes, but slightly more patients with kidney disease. But these were only minimal differences, and the authors took those differences into account, making adjustments for them in their findings.

Yet there were two differences between the female and male doctors that may be of substance: the physicians themselves. Female physicians in the study were on average 5 years younger than their male counterparts (42.8 years versus 47.8 years). Not to be ageist, but younger doctors may have a greater ability to use hospital computer systems, may be more likely to utilize social services for their patients, and may be more willing to alter their practices based on the latest studies.

Another important aspect is that female physicians on average took care of fewer hospitalized patients than their male counterparts, with female internists taking care of an estimated 132 hospitalized patients per year versus male internists' 181. The busier schedule of the male internists may increase the chances that some aspects of care will be negatively affected. The authors tried to correct for both the age and patient load issues, but that's not easy to do.

As provocative as this new study is, it's far from conclusive. A 2013 study in the Journal of the American Board of Family Medicine found no differences in care between male and female physicians in the rates of death, hospitalizations or health care expenditures.

In summation, this research does nonetheless offer a reminder to all physicians, regardless of gender or age, that many factors affect patient death rates and readmissions -- and we can't afford to let any of them fall through the cracks.

Tomorrow, my colleagues Dr. Glazier and Dr. Ko will cover this study.

(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.)