What is known about testosterone and cardiovascular biomarkers
Most previous studies investigating the relation between testosterone and cardiovascular risk have looked at “hard clinical endpoints” such as myocardial infarction and stroke to determine risk. While effects on hard clinical endpoints is the gold standard outcome in medical research, it is not resource intensive to conduct such studies. Therefore, analyzing effects on risk factors and biomarkers that contribute to the development of heart disease and stroke, or signal presence of cardiovascular pathology, is a more feasible study approach. Analyzing the effects of testosterone deficiency and testosterone therapy on risk factors and biomarkers will also help discard the conclusions from the flawed studies that alleged cardiovascular risks, and support the growing number of studies which demonstrated cardiovascular safety – and even benefits – of testosterone therapy. 3-13,15,16,23
The Institute of Medicine (IOM) defines biomarkers as “indicators of normal biological processes, pathogenic processes or pharmacologic responses to an intervention”.24 When biomarkers are used as proxies for clinical endpoints, they are referred to as surrogate endpoints and provide the utility of evaluating interventions more efficiently and quickly. They are particularly important when the effect of a drug is expected to take extensive time to become manifest. This is the case with testosterone therapy.
Besides traditional biomarkers such as high-density lipoprotein cholesterol (HDL), high-sensitivity C-reactive protein (hs-CRP), glycated hemoglobin (HbA1c), several new biomarkers have been linked to cardiovascular disease mechanisms, as outlined in the table.
What this study adds
10,041 male patients were identified in the database of a commercial clinical laboratory performing biomarker testing.22 Patients were grouped by total testosterone levels and associations with 10 biomarkers – also known as cardiovascular risk markers - were determined. Included in this panel of biomarkers were HDL (the “good cholesterol”), glycated hemoglobin (an index of average blood sugar levels over the past 3 months), CRP (an inflammatory marker) and leptin (a satiety hormone that is produced by the body's fat cells).
The men’s age was 58 years (range = 48-68), and testosterone level of 14.6 nmol/L (range = 10.5 – 19.6 nmol/L). An inverse relation between testosterone levels and cardiovascular risk was seen for 9 of 10 biomarkers, including the ones just mentioned; in other words, the lower the testosterone level, the worse the biomarker profile.
The practical implication of these results is that men with low testosterone levels could be at increased risk for cardiovascular disease as seen by deleterious changes in cardiovascular risk markers.22 This is consistent with previous studies showing that men with testosterone deficiency are at increased risk of cardiovascular disease and mortality.16,19,20
This is the first study to examine cardiovascular risk associated with testosterone levels using a large panel of 10 biomarkers that have been linked to cardiovascular health.22 It should be noted that this was a “snap-shot” study looking at the relation between testosterone levels and deleterious changes in cardiovascular risk markers (biomarkers). It did not investigate the effect of testosterone therapy on changes in these risk markers, it merely demonstrated that low testosterone levels are associated with deleterious changes in risk markers for cardiovascular disease. Considering the multiple studies showing that testosterone therapy reduces cardiovascular and all-cause mortality 3-13,15,16,23,25, testosterone therapy should lead to improvement in cardiovascular risk markers.
One of the highly publicized flawed studies alleged increased risk of heart attack following start of testosterone therapy prescription.26 If one accepts the idea that testosterone therapy leads to early heart disease complications, there must be a mechanism that would lead to heart attack in as early as 3 months, as alleged to in one of the flawed studies.2 Since testosterone therapy does not cause progression of atherosclerosis 27 - in men not taking statins, one marker of atherosclerosis (calcium score) was actually significantly lower in the testosterone group than in the placebo group 27 - a more likely mechanism in this short timeframe would be through worsening of endothelial function.28 Endothelial dysfunction means that blood vessels in the body have become dysfunctional and tend to constrict excessively as well as release substances that contribute to development of atherosclerosis and inflammation. Endothelial dysfunction is a marker of atherosclerosis 29, and a well-established response to cardiovascular risk factors that precedes the development of atherosclerosis.30,31
A recent study specifically looked at the effect of testosterone therapy on endothelial dysfunction.32 Endothelial function was measured in hypogonadal men prior to and at least 3 months after initiation of testosterone therapy.32 23 male patients with symptoms of hypogonadism, a total testosterone level of <350 ng/dL, and who planned to begin testosterone therapy, were included in the study. It was found that men with symptomatic hypogonadism often have abnormal endothelial function, and that testosterone therapy improves endothelial function in the majority of men, and remains unchanged only in a minority.32 Importantly, no subject in this study experienced a significant worsening of endothelial function after testosterone therapy. These study clearly refute the flawed study by Finkle et al. and supports the growing number of studies showing cardiovascular benefits with testosterone therapy 16,33-35, and the position by the European Medicine Agency that testosterone therapy is safe.36
Regarding leptin, other studies have confirmed that testosterone treatment reduces leptin levels.37-39
The reduction in leptin levels, which suggest a reduction in leptin resistance (or improved leptin sensitivity), is especially notable. Currently there is no established treatment for leptin resistance, a condition for which treatment is needed.40 Considering that leptin resistance may play a causative role in the metabolic decline seen with aging 41, the improvement of leptin sensitivity with testosterone treatment is especially notable.