When Are Men Most Fertile?

The first chapter of a classical medical text from Han dynasty provides a fertility timeline for both genders.

Nice thumbnail, even nicer content 🙂

The most fertile age for females can be found over at this post.

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I am passionate about history of medicine from East Asia and ways to connect the ancient knowledge of health to achieve longevity.

What book are we reading today?

The classical text I’m referring to is called Basic Questions, which is considered to be the fundamental source for Traditional Chinese Medicine (TCM) since Han dynasty (3rd century BCE – 3rd century CE)

It covers the theoretical foundation and diagnostic methods and is also a major book of Daoist theory and lifestyle.

Eastern philosophy of Yin Yang and Five Phases principles are underlying structures we need to comprehend in order to properly analyze this text

Essentially, it’s the belief that human beings are microcosm of the cosmos and that the external changes directly reflect our internal condition.

The book explores the reasons for diseases, which mostly come from environment, emotions, diet, and age.

The very first chapter of this book asks the question: Why do we become less fertile as we get older?

Translation of the text:

Male of eight years 

腎氣實, 髮長齒更 
Kidney energy fills, hair grows, and teeth erupt
二八, 腎氣盛 
By second eight (age 16), kidney energy flourishes
天癸至, 精氣溢瀉
Heavenly fluid arrives, Essential energy overflows
陰陽和, 故能有子 
Yin Yang in harmony (= coitus) is the reason he can have a child

Energy from the kidneys is considered to be the primal force for the body.

It is originally responsible for growth and reproductive development. Kidney’s energy governs bones, teeth, marrow, and hair.

Heavenly fluid (天癸), when used for the females, indicate menses.

However, both male and female possess heavenly fluid.

It’s best to interpret this term as a reproductive secretions that allow conception to take place.

Essential energy is the energetic nature of Essence, which is stored in the kidneys. Essence governs birth, growth, reproduction, and development.

In modern science, it’s comparable to all genetic expressions of our physical appearance.

三八, 腎氣平均 
By third eight (age 24), kidney energy is in balance
Tendons and bones are firm and strong

Hence true molar (wisdom teeth) erupt 

Growth is at its ultimate

四八, 筋骨隆盛 
By fourth eight (age 32), tendons and bones thrive

Muscles and flesh are full and robust

These are some of our best fertile years… would you agree? 😉

五八, 腎氣衰 
By fifth eight (age 40), kidney energy weakens

Hair falls out and teeth wither

六八, 陽氣衰 
By sixth eight (age 48), Yang energy weakens

竭於上面焦, 髮鬢斑白. 
Face is scorched (dried up), hair and sideburns whiten

From here on, the decline begins. In Yin Yang principles, Yang is thought to be masculine, and Yin is feminine.

So by late 40’s we start to experience weakening of the male energy. Could it be related to testosterone?

Also, once we start to see hair falling out and teeth getting brittle, we could think that the kidney energy is not as prosperous as it once was.

七八, 肝氣衰
By seventh eight (age 56), liver energy weakens
Tendons are not skilled at movement
Heavenly fluid depletes and Essence diminishes
腎藏衰, 形體皆極
Kidneys weaken, and the bodily form is at its ultimate
By eighth eight (age 64), hair and teeth are soon gone.

Liver energy is smoothly flowing in nature and governs movement of tendons and sinews. Weak liver energy could make us less flexible in range of motion.


Like with all the medical texts, we should take this classical excerpt with a grain of salt.

This 2000+ year old knowledge is a useful reference for how our ancestors saw the rise and fall of human body, but fortunately we live in a time when conscious changes to our lifestyle to eat healthier, sleep better, and relax more can significantly prolong our physical strength, appearance, and reproductive health.

We got this fellas!

Thank you for reading,


eternal student of life

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