DEAR DR. ROACH: My doctor prescribed a statin for me to reduce my LDL cholesterol, which was at 131. My HDL was 70. I stopped taking it after three weeks because I was experiencing pulled muscles at the top of each hamstring. I run 20 miles a week. Thirty-five years of running and this had never happened. Now, two years later, I read an article about milk thistle reducing LDL. I began taking it daily three months ago, and at my annual physical two weeks ago my blood test results showed a reduction in LDL to 105 and HDL at 71. My doctor and I were surprised and pleased. The only difference in my lifestyle was the milk thistle. Have you had any experience with patients reducing LDL when taking a milk thistle supplement? — Anon.

ANSWER: Milk thistle has been shown to reduce LDL cholesterol. The best evidence comes from people who also had diabetes. However, it is unknown whether milk thistle provides the same benefit in reducing heart disease risk that statins do. Not all treatments that reduce cholesterol are proven to reduce the risk of heart attack.

Because supplements are not regulated the way prescription drugs are, you are reliant on the manufacturer’s word that they are providing you with the correct product. A 2019 review of available milk thistle products showed dramatic variability in the amount of the active ingredients and levels of pesticide residuals, mycotoxins and bacterial contamination.

Despite some benefit seen in trials, the poor quality of available products in the U.S. prevents me from recommending milk thistle as treatment to lower LDL. I’d recommend considering a trial of a different statin. Pravastatin, fluvastatin and pitavastatin have lower risk of muscle effects than other statins.

DEAR DR. ROACH: I take Prolia every six months for osteoporosis/osteopenia. My endocrinologist tells me that this makes me susceptible to UTIs and respiratory tract infections, which seems to imply that Prolia might have some immunosuppressive effects. Does it only act against osteoclasts and bone resorption? How would being on Prolia affect the immune response to COVID-19 vaccination? — L.I.

ANSWER: Denosumab (Prolia) is a monoclonal antibody that blocks the receptor activator of nuclear factor kappa-B ligand (RANKL). One effect of this blockage is to prevent the formation, function and survival of the bone-absorbing cells, the osteoclasts. However, RANKL also has effects on the immune system, and some, but not all, trials showed an increase in infections such as pneumonia, skin infection and diverticulitis. The number of people affected was small.

I think your endocrinologist was being very cautious in telling you about the possible increased risk of infection, which may not exist at all, and if it does, appears to be small.

Because there are no data on effectiveness of the COVID-19 vaccine in people taking Prolia, I cannot answer for certain. However, because the degree of immunosuppression, if any, appears to be small, I don’t think it is likely that Prolia would create a meaningful decrease in the effectiveness of the vaccine. Certainly you will be safer having gotten the vaccine than if you had not done so. It would be wise to continue to be cautious even after vaccination while there is still ongoing transmission in the community.

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Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to [email protected] or send mail to 628 Virginia Dr., Orlando, FL 32803.