Free testosterone levels by age might be on the decline.
We know that free testosterone and bioavailable testosterone are key for feeling androgenic. You can have all the testosterone in the world, but if you’re body can’t use it, then it’s no good.
In my previous article, I showed that total testosterone doesn’t necessarily decrease with age. But it might be slightly different for free testosterone.
According to researcher Henry Feldman back in 2002, both free and albumin-bound testosterone declines at about 2-3 %/yr, while sex hormone-binding globulin increases at 1.6 %/yr (R). So clearly, free testosterone drops faster than total T. Or differently put, total testosterone can remain the same while free testosterone drops.
What is free testosterone?
Free testosterone is the amount of testosterone not bound to any carrier proteins. Usually, labs calculate free testosterone (instead of directly measuring it) by testing for total testosterone, SHBG and albumin. Then with the help of a formula, it gives you your free testosterone.
Free testosterone is the testosterone that your body can use. Testosterone has to enter the cell and bind to the androgen receptor (AR). Once it’s bound to the AR, it can stimulate changes in the body (e.g. muscle growth).
Testosterone binds to carrier proteins such as albumin, sex hormone-binding globulin (SHBG), cortisol-binding globulin, and orosomucoid.
But be aware, calculated free testosterone (cFT) can be very inaccurate.
Here are 4 reasons why:
- Albumin only binds loosely to testosterone (so it’s still considered bioavailable)
- SHBG-bound testosterone can still be taken up by cells by megalin to exert actions
- SHBG has a binding affinity, which means that you can have super high SHBG, but they don’t really bind to T, or you could have only a low amount of SHBG, but they potently bind up androgens.
- SHBG can have different half-lives. Meaning, 1 SHBG molecule can have a half-life of 5 days and another a 10-day half-life. The longer it floats around, the longer your T will be unavailable.
So calculated free testosterone is a far cry from bioavailable testosterone. I don’t want to go too in-depth in this article so let’s move on.
Why free testosterone matters
Free testosterone doesn’t actually matter that much. What we really want to look at is bioavailable testosterone (BT). This includes free and albumin-bound testosterone. You get calculated and assayed BT (cBT and aBT). Assayed BT directly tests BT whereas cBT is again, calculated. Oftentimes, you might see that your cBT is normal, but aBT will be super low.
Regardless, many studies have been done looking at total and free testosterone and free testosterone still matters.
Free testosterone correlates with bone mineral density, muscle mass, and muscle strength, and is inversely associated with various diseases, cancers and all-cause mortality.
Testosterone is amazing, mkay?!
Free testosterone levels by age
Study 1 – (Free testosterone levels by age in China)
In 2013 in China, 1213 adult men of all ages were tested for their total and free testosterone as well as SHBG (R).
What they found was that SHBG tends to go up with age and free testosterone tends to go down.
As a result, LH goes up.
Higher LH often times correlates with impaired testicular function. Thus more LH is required for the same output.
Study 2 – (Free testosterone levels by age in Baltimore)
444 men from Baltimore between the ages of 30–96 got their hormones tested (R).
Even though testosterone remained more or less the same over all ages, SHBG tended to increase and free testosterone decreased.
Study 3 – (Free testosterone levels by age in Australia)
61,131 men between 2007–2013 in Melbourne and central Victoria Australia were tested for their hormones and here’s what they found (R).
SHBG tended to increase and free testosterone decreased. See a recurring trend here.
Why are free testosterone levels by age going down?
An increase in SHBG seems to be an effect/cause of aging… But is it normal? I’d say no.
There are likely 4 main reasons why SHBG is going up with age.
#1 Not eating enough calories
As men age, their appetites tend to decrease and they eat less and less (R). Eating too little can lead to a decrease in total, but especially free testosterone.
#2 Not eating enough protein
Protein (red meat) in general is hard to digest and might get more difficult as you age. Eating enough protein helps to keep SHBG low (R). On the flip side, a carnivore diet is more likely to increase SHBG and lower free T. That’s why low libido and ED are common among carnivores.
#3 Nutritional deficiencies
As protein consumption goes down, so does vitamin and mineral intake. Protein-rich foods (organ meat, eggs, shellfish, muscle meat, etc.), are the richest sources of vitamins and minerals. Nutritional deficiencies are more common in the elderly than in the young.
#4 Adrenal insufficiency
DHEA and DHEA-S (adrenal steroids) drop more aggressively with age than free testosterone. Free testosterone drops by about 2% per year and DHEA and DHEA-S drop by 3.1% and 2.2%, respectively, per year (R).
Why is this important?
Because the marked decrease in DHEA formation by the adrenals leads to a decrease of about 50% in total androgens in men between the ages of 40-80 years (R).
Testosterone and DHT are markers of testicular hormones and account for about 50-70% of the total androgens in the male body. DHEA, DHEA-S, androstenedione, androstenediol, androstanediol, androsterone, etc, are lesser-known steroids that make up the other 30-50% of the total androgen pool.
These steroids also bind to SHBG, which means more bioavailable testosterone.
A drop in DHEA and androstanediol (5-alpha reduced steroid) reduces bioavailable testosterone to a much greater extent than just low DHEA itself (R). It’s been found that men with normal testosterone and low androsterone (5-alpha reduced steroid from DHEA) have low libido compared to those with normal/high testosterone and androsterone.
As you can see in this graph below, total testosterone remains the same, while bioavailable testosterone (BT) drops as 5-diol (aka androstanediol) drops.
As you can also see in this graph, DHEA and androsterone drop more aggressively with age, whereas DHT remains more or less the same. This drop in androstenediol, androstenedione, DHEA and androsterone will reduce bioavailable testosterone and contribute to symptoms of low testosterone.
One of the best ways to increase androstenedione, androstenediol, DHEA, androstanediol and androsterone is by using topical DHEA (R).
Topical DHEA is much better at increasing these steroids than oral DHEA.
I prefer this product. But you can also make your own by mixing DHEA powder with ethanol.
Why is my SHBG going down as I age?
On the flip side, some people experience a decline in SHBG and an increase in free T as they age.
This is predominantly due to:
- Excessive weight gain and obesity
- Diabetes and hyperinsulinemia
- Check your cholesterol, triglycerides, fasting glucose, fasting insulin, C-peptide and HbA1c
- Fatty liver (or just dysfunctional liver in general)
- Check liver enzymes such as ALT, AST and GGT
Summary
Free testosterone is more likely to decrease compared to total testosterone. The main reason for this is diet. Eating a poor diet will lead to nutritional deficiencies, health complications, adrenal insufficiency and a massive drop in bioavailable testosterone.
Doing a test for total and calculated free testosterone is definitely not good enough. If you have normal total and free testosterone, but you still feel suboptimal, your bioavailable testosterone is still likely too low. You can do a DUTCH test (which is a urinary test for many different androgens) or you can do blood tests for:
- Total testosterone
- DHEA
- DHEA-S
- DHT
- SHBG
- Fasting insulin and C-peptide
- Albumin
This will give you a better picture of bioavailable testosterone than calculated free testosterone only.
The best way to directly measure free testosterone is with equilibrium dialysis. However, not many labs offer this because it’s expensive and labor-intensive.
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