Last week I caught my first cold of 2016. I know, first world problem, right? But in typical introvert fashion, it made me reflect.

To be clear, I wasn't reflecting in a melodramatic, Nancy Kerrigan "Why me?" sort of way. Instead, I wondered why I've only been sick once in 10 months, while others will tell me how they're constantly getting sick. I also remember hearing that "having 4 or more colds a year is normal."

Yeah, about that.

While I'm not a doctor, the immune system is really complex with many moving parts that keep it healthy. And of those parts, I've seen a strong correlation between someone's sleep, nutrition and stress levels.

To start, the link between nutrition and immune health is relatively easy to understand. Study after study has illustrated that vitamins, minerals, and antioxidants are all much more potent and bioavailable in foods than in pill form. That doesn't mean you need to have a mixing bowl of salad for lunch everyday like yours truly. But it does mean that you can't expect to have a healthy output (immune health) if you're not feeding it healthy input (fruits and vegetables).

Like nutrition, sleep also has a clear link to immune health. Besides the anecdotal tales of "sleeping it off," there's ample evidence of sleep deprivation leading to immune suppression. Of course, getting more sleep is easier said than done, as both bosses and spouses love nothing more than to hear the words, "I'm off to bed to give my immune system a boost!" But whatever way you can, increasing your sleep is an integral part of health.

Finally, we get to stress and the main point I want to make: that "stress" is much more encompassing than we think.

For example, we tend to think of stress like "The Chicken Roaster" episode of Seinfeld. We'll associate it with work, busy schedules, or worrying about the upcoming election. But we often forget that stress comes from these sources as well:

-Lack of sleep

-Having a few too many adult beverages

-Poor diet choices

-Being constantly "on" and married to your smartphone

-Intense physical exercise

Add to the fact that some people are predisposed to having higher stress levels, it's no wonder why their immune system might not be at full strength. The book Why Zebras Don't Get Ulcers is a great resource on this topic, but be warned that it may make you stressed about your stress.

That's where something like Heart Rate Variability (HRV) can help you understand your body and your stress levels. Put simply, HRV is a terrific way to measure your sympathetic (fight or flight) or parasympathetic (rest and digest) tone. We'll never be fully in one category, but if you're too sympathetic, you're going to be "on" all the time and likely sick more often.

To the right is a screenshot of my own HRV scores, and you can see the slow, downward trend as well as the "High" monthly load sign. The nine point spike I had just before I became symptomatic is also explained with research on the topic, as your body attempts to make itself more parasympathetic during the incubation phase. But beyond that, HRV has made me understand my body better and illustrate that everything matters.

We all have our own reasons to stay healthy - which for me is the pursuit of a bigger deadlift and kettlebell press. But whatever your reasons, there's more to staying healthy than chomping away on a few vitamin C tablets.