6LETTERS

 In Search of the Sixth Vital Sign

by Senior's Know-How l May 11, 2026

We live among countless numbers every day. 

Heart rate, blood pressure, blood sugar, body temperature, oxygen saturation. 

In hospitals, these are called the five 

"Vital Signs." 

This is because they are the signals that most fundamentally show a person's life and health status.

However, for a long time, 

I have had this thought:

"Why aren't hormones—

which actually have the greatest impact on 

a person's life, emotions, energy, aging, sleep, and stress—

treated like vital signs?"

 

 

For the past 20-plus years, 

I have worked in the pharmaceutical and digital healthcare industries in drug development, 

clinical trials, medical devices, business development, and marketing. 

In that process, 

I met numerous patients, doctors, and researchers, 

and experienced both success and failure. 

But as time passed, what remained in my head was not flashy numbers or revenue, 

but ultimately the "patients."

When I was working at a pharmaceutical company, 

I lived among countless documents—

designing clinical trials, reviewing medical records, 

and preparing for MFDS (Ministry of Food and Drug Safety) inspections and global audits. 

When doing so, at some point, you forget the truly important essence. 

Although I started it as work for patients, 

there were times when patients felt like just numbers on documents.

Then one day, 

I came across the "Save the Heart in Africa" project, 

which was one of the global social contribution programs conducted by the company. 

At first, to be honest, I had doubts: 

"In Africa, aren't food, drinking water, and basic medicines more urgent?" 

But after talking directly with the person in charge who created the project, 

my thoughts changed completely.

That person noticed the fact that the incidence rate of cardiovascular disease 

in the African population was very high while analyzing global statistics, 

and realized that the prejudice people vaguely hold—

'poor countries need food first'—

was hiding the medical reality. 

It was a story that for someone, early detection of hypertension and cardiovascular disease could be survival itself.

With that event as a turning point, I started asking myself questions:

"Am I really thinking patient-first?" 

"What am I missing?"

 

Since then, I have conducted various projects such as a campaign for gastroesophageal reflux disease patients, 

an awareness improvement campaign for drug side effects in arthritis patients, and a public interest campaign for depression patients. 

In particular, the "Band-Aid for the Mind, Blue Band" campaign, 

which was conducted together with the Korean Neuropsychiatric Association at a digital healthcare startup, 

remains one of the most memorable experiences for me. 

Seeing the reality where depression patients could not access new treatment information, 

I deeply felt that technology alone cannot change the world. 

Ultimately, what was important was 

"accessibility."

And that deliberation eventually led to the realm of 

"hormones."

Testosterone, estrogen, progesterone, melatonin, insulin, cortisol. 

Hormones constantly regulate our body and emotions. 

Sleep and fatigue, stress and depression, focus and libido, 

and even aging and hair loss are ultimately deeply connected to hormones. 

Yet, most people live without measuring their hormones at all.

Why is that?

Because it is too difficult, expensive, and inconvenient.

You have to go to a hospital, get blood drawn, and wait for the test results. 

But the bigger problem is that even the results measured with such difficulty may actually not be perfect. 

This is because hormones constantly fluctuate throughout the day. 

For example, 

testosterone, a male hormone, is generally highest in the morning and decreases toward the evening. 

Melatonin increases at night, and insulin changes significantly after meals. 

It changes continuously even within the same person, 

and the patterns are different for everyone.

Then, can a single test really accurately explain our body's condition?

I gradually came to think, 

"Aren't hormones biological signals that need to be observed continuously?" 

Just as continuous glucose monitors changed the paradigm of blood sugar management.

At the end of that question, I eventually decided to start a company.

The company name is 6Letters. 

"Make a Meaningful Difference for Your Healthy Life."

It means making a meaningful change in your health.

And now, I am creating technology to understand hormone changes more easily and continuously 

through wearable devices like smartwatches. 

There are still many deficiencies and many problems to solve. 

However, I believe that one day, an era will come when anyone can understand 

their body's condition more easily and manage their health on their own even before diseases occur.

I think that is the beginning of the "Sixth Vital Sign."

In this space moving forward, rather than just simple startup stories, 

I plan to slowly talk about hormones and humans, technology and medicine, 

and the signals inside our bodies that we did not know well yet.

A journey to find invisible hormones. 

I now begin that first story.