First, a dose-dependent response and long-term observation with higher sample size. Most of the interventional studies with the above-mentioned CR-mimetics lack the dose response relationship with long term effects. They have focused on traditional cardiovascular risk factors, such as obesity, hypertension, and hyperlipidemia[
32,
223,
237], without considering the cardiovascular endpoints, such as age-related atrial wall stiffness and flow-mediated dilation. In addition, bioavailability and metabolization are important factors for designing clinical experiments and ensuring therapeutic efficacy. Low oral bioavailability may be a major challenge associated with the ambiguous therapeutic effects in clinical trials, from positive[
42,
44] to ineffectual[
238-
240] or large individual variations[
228]. Factors causing low bioavailability may include not only their content in the diet and intake in humans, but also their metabolic processes mediated by the liver, intestines and microbiota[
241]. As an example, dietary intake levels of total flavanols are estimated to vary greatly from 386 mg/d in Germany[
242], 192 mg/d in the United States[
243], and 23 mg/d in the Netherlands[
244]. Likewise, daily intake of spermidine is reported to correlate with gross domestic product[
245]. These discrepancies cause problems for estimating an efficient intake, which certainly influence dosing schemes and clinical outcomes. With respect to absorption, the forms displaying in circulation are often not the forms seen in food, indicating that absorption is accompanied by certain conjugation and metabolism. As an example, quercetin in a form of glucoside in onions is efficiently absorbed and bioavailable compared to the free forms[
246] or other forms containing rutin in apples and tea[
247]. In contrast, plasma EGCG is mostly in an unconjugated form, and has proven to have higher activity than its metabolites[
248]. Lastly, a combinational therapy should be considered. Biological cardiac aging is a multifactorial process with many systemic contributing mechanisms occurring within the heart and surrounding tissues. As such, it is unlikely that any single pathway or intervention would fully restore age-related cardiac phenotypes. It has been demonstrated that the impact of combinational therapies on boosting the functional abilities of vasculature and endothelial function is greater than those of individual treatments in postmenopausal women[
249,
250]. Based on the observation that curcumin pharmacokinetics are affected by sex[
251], we propose that the dosage of polyphenol or polyamine, personalized as a “one‐dose‐fits‐all” strategy, is unlikely to work. Thus, as an example of combinational therapies, we propose that stimulating glucose oxidation, by pyruvate dehydrogenase kinase inhibitor[
252], along with a supplementation of polyphenol or polyamine, may be beneficial to human aging hearts[
253]. The concept is that glycolysis is increased in the aged heart along with unaltered glucose oxidation[
14,
254]. As a result, glycolytic intermediates are diverted to form advanced glycation end-products[
255] (
Fig. 1b), which can be recognized by CD36[
256] causing oxidative stress-related inflammation and endothelial dysfunction[
257,
258]. Thus, stimulating glucose oxidation will amplify the effect of CR-mimetics by enhancing ATP production in concert with improving systemic glucose tolerance and inflammation. This notion can be further supported by others showing that a combination of spermidine from a natural product with nicotinamide inhibits oxidative stress and improves endothelial cell survival, in a potentiated manner than each compound alone, in platelets isolated from patients with metabolic syndrome[
259]. This also holds true for the effect of combinational resveratrol-piperine with α-tocopherol (has an anti-inflammatory activity[
260]), in a clinical trial[
47], in which, the decrease in arterial hypertension and inflammation is evident in older patients [age (68±4.7) years] with metabolic syndrome[
47].