The ZRT Laboratory Blog

The ZRT Blog is an extensive resource for patients and health care providers searching for health and hormone testing information. Here, you can read about ZRT’s cutting edge research, advances in testing, wellness advice, and health industry highlights.



Dr. David Zava

David Zava, PhD is the founder, CEO and Chief Scientist at ZRT Laboratory. He has been instrumental in developing research projects with physicians and academic groups to understand the role of steroid hormones in health and disease for the past decade.
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Recent Posts

Cortisol Testing in Saliva, Blood & Urine

Posted by Dr. David Zava on Friday, 29 May

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Practice Takeaway: Providers should be aware that three different body fluids – saliva, blood or urine – can be used to assess adrenal gland function, and should know each method’s advantages and disadvantages, when deciding how to test patients.

Inadequate or excessive production or disrupted circadian patterns of cortisol synthesis by the adrenal glands in response to stressors can eventually lead to imbalances in blood glucose levels, impaired immune response, as well as a host of different hormonal imbalances, all of which are associated with multiple adverse conditions and symptoms.   

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Flaws in the Iodine Loading Dose Urine Test

Posted by Dr. David Zava on Thursday, 18 December

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I began the study of iodine because I believe it has benefits to human health. As a breast cancer researcher I believe that iodine protects the breasts and uterus against toxic and mutagenic estrogen metabolites that form in some people more than others. Thus, choosing the most reliable test to a) determine iodine status, and, b) supplementation to maintain levels seen in populations with lowest rates of breast cancer (ie. the Japanese), is a key health consideration with or without breast cancer risk factors.

That leads us to the all-important discussion of iodine testing methods. Have you ever had your levels evaluated with a 24-hour iodine loading test and been found to be deficient? If so, you are not alone. This is a test where 98-99% of people who take it will be deemed “whole body iodine deficient”. On the basis of this test result, you may be advised to take iodine supplements at a dose that makes some people ill, and raises iodine to hundreds of times the levels recommended by health organizations around the world. In the most serious cases, the dosing recommended to get you to “whole body iodine sufficiency” may cause your thyroid to stop working normally, producing either too much (hyperthyroid) or too little (hypothyroid) thyroid hormone.

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Testosterone: Elixir or Dangerous Drug?

Posted by Dr. David Zava on Wednesday, 19 September

ThinkstockPhotos-85447820_lores.jpgAn FDA-approved testosterone gel was shown to significantly increase risk for adverse cardiovascular, respiratory, and dermatological events in men 65 or older who had impaired mobility and increased health risks.

This is according to a recent study published in the prestigious New England Journal of Medicine (NEJM) (1) that casts a shadow on the common use of testosterone therapy in older men for boosting their energy and vitality. 

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Natural Progesterone as a Preventive for Breast Cancer

Posted by Dr. David Zava on Wednesday, 19 September

ThinkstockPhotos-86519408Editor’s Note: After the publication of Dr. David Zava’s last Health Watchers News and Views post, Hormone and Breast Cancer: the Latest Findings from the WHI, he received an attacking comment from a doctor who has been making claims for years that natural progesterone has the same effects as the synthetic progestins.

Although, as an editor, I do not publish comments that attack, Dr. Zava wrote an eloquent, if technical response which adds to the dialogue about progestins, progesterone and breast cancer. We share it here for the reading pleasure of hormone biochemistry geeks everywhere! 

I very much disagree with the comment that “Progestins cause more breast cancer than estrogens because they act like progesterone.” Yes, synthetic progestins increase breast cancer, but there is no evidence that progesterone does the same. Quite the contrary. Below is my argument in favor of natural progesterone as a preventive for breast cancer, with reference to the Fournier studies that address this issue.

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