Aging is often described as a risk factor for disease (Niccoli and Partridge, 2012). Indeed, the risk for hundreds of diseases, the so called age-related diseases, is increased with age and some of these diseases (such as Alzheimer’s disease) never occur in young people. I and others have argued that aging itself should be called a disease (Bulterijs et al., 2015; Gems, 2011, 2015; Lustgarten, 2016; Zhavoronkov and Bhullar, 2015). Interestingly, aging has been described as a ‘disease complex’ in the older literature (Perlman, 1953).

But can something that increases the risk for disease (a risk factor) be a disease in itself? The answer is undoubtedly yes. Take for example diabetes which is a disease but also increases the risk for various other diseases such as diabetic nephropathy, retinopathy, neuropathy, atherosclerosis, and various cancers. Or the “accelerated aging” disease Hutchinson-Gilford Progeria Syndrome (HGPS) that increases the risk for heart disease.

The US Food and Drug Administration (FDA) defines disease as “damage to an organ, part, structure, or system of the body such that it does not function properly (e.g., cardiovascular disease), or a state of health leading to such dysfunctioning (e.g., hypertension); except that diseases resulting from essential nutrient deficiencies (e.g., scurvy, pellagra) are not included in this definition” (21 CFR 101.93(g)(1)). Aging fits this definition well as most scientists believe that aging is caused by the accumulation of cellular and molecular damage leading to impairment of normal physiological functioning of cells, tissue, organs and bodily systems which in turn causes age-related diseases and increased risk for death (Aunan et al., 2016; Johnson et al., 1999; López-Otín et al., 2013). Furthermore aging is also a risk factor for other diseases (Niccoli and Partridge, 2012). Therefore aging fits the first and the second part of the definition of disease. Finally, aging is not caused by a nutrient deficiency and hence all conditions to label it as a disease are met.

Aging has a 100% mortality rate which puts it in a limited group of diseases that kill all affected individuals. Even a feared disease like ebola only has an average mortality rate of 50% (WHO). The most deadly infectious disease is rabies but even this disease does not reach 100% mortality rate as 14 people so far have been reported to have survived the disease (Manoj et al., 2016). And many inheritable diseases have incomplete penetrance meaning that while some carry the disease gene (to be technically correct we should say allele) they do not become sick (Lobo, 2008). Aging in contrast has complete penetrance and is universally deadly.

One argument used against labelling aging as a disease is that aging is universal among humans. Everyone ages. In contrast ‘classical diseases’ never affect everyone in a population. Though, we should point out that some diseases such as common colds are nearly universal (Caplan, 2005). Let us do a thought experiment (the scenario is biologically impossible; it’s very common for thought experiments to be impossible to actually conduct, rather they are used to think about the implications of what would happen if something was possible). What if humanity was suddenly hit by a pandemic that spread like wildfire through the human population eventually affecting every human on earth. At the early phase before the infection had spread to every person on earth we would call it a disease. Paradoxically, the moment the last human on earth becomes infected we would have to switch our thinking and stop calling the infection a disease as it is now an universal condition among humans. Clearly, this is ridiculous.