Yet Another Reason Not to Be Obese: It Accelerates Immune System Aging

By now, I would hope, the life science horror stories that turn up here on a regular basis will have convinced you that excess body fat is not good for your long term health and longevity. Some of that is the result of the biochemistry of fat tissue en mass, and some of that is the reaction of your metabolism to the sedentary, high-calorie lifestyle required to gain that fat tissue, but the end result isn't pretty. More fat means a lowered life expectancy and a greater risk of all the common age-related diseases - and the decades of suffering in health and wallet that come with them.

Being overweight is a choice for 99.9% of people. A seductive, easy choice to slip into in a wealthy society whilst surrounded by an adundance of food, but a choice nonetheless. You might think of doing something about that.

In any case, today I thought I'd showcase another motivativational piece of research on the consequences of excess body fat, this time as it relates to the degeneration of your immune system. One of the reasons your immune system fades and fails with age is the involution - or shrinkage and atrophy - of the thymus, the organ responsible for sheltering the growing population of T cells:

The immune system undergoes dramatic changes with age - the thymus involutes, particularly from puberty, with the gradual loss of newly produced naive T cells resulting in a restricted T cell receptor repertoire, skewed towards memory cells. Coupled with a similar, though less dramatic age-linked decline in bone marrow function, this translates to a reduction in immune responsiveness

As it turns out, excess body fat speeds this process, to the detriment of health. The immune system performs many vital tasks, such as destruction of senescent or cancerous cells, in addition to dealing with outside threats, and all worsen as the thymus progressively declines:

As the expanding obese population will grow older, their successful immunological aging will be critical to enhancing the health-span. Obesity increases risk of infections and cancer, suggesting adverse effects on immune-surveillance. Here we report that obesity compromises the mechanisms regulating T cell generation via inducing premature thymic involution.

Diet-induced obesity (DIO) reduced thymocyte counts and significantly increased apoptosis of developing T cell populations. Obesity accelerated the age-related reduction [in] recently generated T cells from thymus. Consistent with reduced [T cell creation], dietary obesity led to reduction in peripheral naive T cells

...

In middle-aged humans, progressive adiposity with or without Type-2-Diabetes also compromised thymic output. Collectively, these findings establish that obesity constricts T cell diversity by accelerating age-related thymic involution.

You can't say that you weren't warned.

ResearchBlogging.orgYang H, Youm YH, Vandanmagsar B, Rood J, Kumar KG, Butler AA, & Dixit VD (2009). Obesity accelerates thymic aging. Blood PMID: 19721009

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