*The Function of Ascorbic Acid through Occam's Razor: What We Know, What We Presume… DOI: http://dx.doi.org/10.5772/intechopen.109434*

health conditions: an adequate AsA supply is not a guarantee of good health *per se*, because it must be integrated with other signals. This also means that the huge amount of literature showing that antioxidants have a positive effect on the health of both animals and plants, the effect invariably explained with the simplistic assumption that more antioxidants "kill" harmful ROS, is correct in the observations, but misled in the interpretation.

The hypothesis outlined above also helps in tentatively answering the overwhelming question in the title of this section: why losing AsA biosynthesis? If AsA content is critical to accurately set the "meter" of the response mediated by some regulatory 2-ODDs, "homemade" AsA could alter the baseline of the response. On the contrary, an AsA pool totally depending on the dietary intake provides full information on whether a non-synthesizing individual takes (or not) enough AsA with available food, helping in setting the proper levels of housekeeping stress responses. In years of personalized medicine, the possibility that an organism adjusts its own defenses *à la carte* is quite intriguing and deserves further investigation. In terms of trade-off, losing AsA biosynthetic capability might have resulted in the advantage of accurately setting the alert level for each individual.

A possible testing place for the model of AsA-dependent regulation of basal defense levels comes from the emerging field of ecological immunology. The concept that AsA improves immune defenses is universally accepted, and some studies support this claim, usually explaining the beneficial effects of AsA on the immune system with its antioxidant function [99]. Ecological immunology analyzes different aspects of the immune response, including how stress conditions differently influence immunity in different individuals [100]. The energy cost of immune responses is key to understanding why acute stress conditions can suppress part of defenses diverting energy resources to the activation of "first-line" responses [101]. The relationship between energy and stress and their integration as the driver of complex immune responses resembles the situation described in the model sketched in **Figure 4**.
