Free Androgen Index

What is Free Androgen Index (FAI)?

Androgens are hormones that produce male characteristics, like facial hair and a deep voice^[1]. The most common androgen is testosterone.

The free androgen index (FAI) measures how much biologically active or free testosterone is circulating in the blood. FAI can detect abnormal androgen levels, particularly in women.

Note: If you are on a high dose of biotin therapy (>5mg/day), you should collect your FAI test sample at least 8 hours after your last biotin dose.

Why Test Free Androgen Index?

A free androgen index test is recommended when an excess amount of androgens is suspected in the body. It most commonly affects women and causes symptoms, like facial hair growth (hirsutism) and irregular periods.

You can measure your free androgen index with a female hormone imbalance blood test or a polycystic ovarian syndrome (PCOS) blood test.

In men, low androgen levels can affect sex drive and are common in men with type 2 diabetes. Free androgen index in men is measured as part of our advanced and ultimate health checks.

What is the Optimal Range?

The optimal free androgen index range for women is 0.19 to 3.63%. For men, it is 35 to 92.6%.

Data collected from Forth customers shows that the average FAI for women is 3.9% and 93% for men. The graph below shows the average FAI by age and sex.

The graph shows that the free androgen index peaks in men aged 30 to 39 before steadily declining.

What Causes High Androgen Levels in Women?

The most common cause of high androgen levels in women is polycystic ovary syndrome (PCOS). PCOS affects approximately 10% of women^[2] and is a condition that is characterised by an overproduction of testosterone by the ovaries. It can be distinguished by at least two of the following; high androgen levels, irregular periods, polycystic ovaries, or high anti-mullerian hormone (AMH) levels^[3].

PCOS is associated with several other conditions, including:

• Infertility
• Obesity and metabolic syndrome
• Heart disease
• Depression
• Endometrial cancer^[4]

Other causes of hyperandrogenism are:

• Congenital adrenal hyperplasia: a group of inherited conditions affecting the adrenal glands, resulting in low cortisol and increased androgen levels^[5].
• Cushing disease: a condition often caused by a benign pituitary gland tumour, causing the gland to release too much adrenocorticotropic hormone (ACTH). ACTH causes excess cortisol and androgen levels^[6].
• Adrenal tumours

Symptoms of High Androgen Levels in Women

Common symptoms of high androgen levels in women are:

• Irregular periods or no periods
• Weight gain
• Thin hair or hair loss
• Excessive hair growth on the face, chest, back, or buttocks
• Acne
• Difficulty getting pregnant^[7]

What Causes Low Androgen Levels in Women?

Low testosterone or androgen levels are a common side effect of getting older in women. They naturally decline with age, some women may not notice the effects while others may be very sensitive to the change. Premenopausal women produce three times as much testosterone as oestrogen.

Other causes of low androgen levels in women include:

• Surgery to remove one or both ovaries (oophorectomy)
• Surgery to remove the adrenal gland (adrenalectomy)
• Adrenal disease
• Pituitary disease
• Premature ovarian failure
• Turner’s syndrome
• HIV infection
• Medications e.g. high doses of corticosteroids or oestrogen preparations such as the pill or HRT^[9]

Symptoms of Low Androgens in Women

The most common androgen deficiency symptoms are:

• Low sex drive, sexual enjoyment, and arousal
• Reduced pubic hair
• Low bone mass
• Loss of muscle mass
• Reduced quality of life (low mood, lack of energy)
• Increased or frequent vasomotor symptoms such as night sweats and hot flashes
• Insomnia
• Depression
• Headaches^[10]

What Causes High Androgens in Men?

It’s rare for androgen levels to become too high in men. Often the cause is medication or supplements, such as anabolic steroids.

Anabolic steroids are a synthetic version of the male hormone, testosterone and can have a powerful effect on the body like increasing muscle mass^[11]. They are often used to enhance sports performance.

Certain cancers may also cause a rise in androgens, particularly testosterone. Recent research suggests that men with a higher level of free testosterone and a growth hormone called IGF-I were more likely to be diagnosed with prostate cancer^[12]. Rarely, high androgen and oestrogen levels in men are associated with testicular cancer, more specifically Leydig cell tumours^[13].

Symptoms of High Free Androgen in Men

The effects of hyperandrogenism in men will depend on the cause. For example, if the adrenal glands cause excess hormones, there will be few side effects, but it can reduce the function of the testes and cause infertility.

If high androgen levels are caused by anabolic steroid use, the symptoms can include:

• Infertility
• Low sperm count
• Erectile dysfunction
• Shrunken testicles
• Hair loss
• Breast development
• Acne
• Stomach pain^[14]

What Causes Low Free Androgen Index in Men?

A low free androgen index in men below 35 can indicate testosterone deficiency. Age-associated testosterone deficiency syndrome, also known as late-onset hypogonadism, is a clinical condition that’s linked to increasing age. It is diagnosed when the blood testosterone level is below the reference range for young healthy adult males^[15].

Interestingly, low testosterone levels are also commonly associated with type 2 diabetes^[16]. Some research suggests that higher testosterone levels can reduce the risk of type 2 diabetes in men, so testosterone is a protective factor against metabolic disease^[17].

Symptoms of Low Free Androgen in Men

Common symptoms of late-onset hypogonadism include:

• Depression
• Concentration issues
• Hot flushes
• Fatigue
• Reduced muscle mass
• Muscle weakness
• Hair loss^[14]

How to Lower Your Androgen Levels

Although little scientific evidence supports the claims, several foods have been suggested to help lower testosterone levels in women. They include:

• Vegetable oils: An increased omega-3 polyunsaturated fatty acid intake has been positively linked with testicular volume in young men. Omega-3s are found in foods like oily fish, soybean oil, flaxseeds, and walnuts^[18].
• Spearmint tea: Some studies suggest that spearmint tea has anti-androgenic effects which could be beneficial for women with PCOS. Animal studies have shown a combination of flaxseed and spearmint extract could reduce testosterone levels and increase oestrogen and progesterone which may contribute to regulating menstrual cycles in women with PCOS.
• Red reishi mushrooms: Reishi mushrooms have been used for centuries in Asian medicine to promote health and support the immune system. Red reishi mushrooms lower 5-alpha reductase, an enzyme that aids the conversion of testosterone to active dihydrotestosterone (DHT)^[19]. Therefore, they may have the potential to lower testosterone levels.
• Liquorice root: A common ingredient in sweets and drinks, consuming 7g of liquorice root daily reduced testosterone levels by a quarter in men after a week^[20]. Similar results have been demonstrated in women, meaning it could be beneficial for PCOS^[21].

Does vitamin D reduce androgens?

Some research has reported a significant benefit of vitamin D supplementation on male hormone concentrations^[22]. A study published in 2021 found that vitamin D supplementation lowers hirsutism scores and androgen levels in overweight women with PCOS^[23].

Our data shows that 57% of UK adults are deficient in vitamin D. The NHS recommends that all UK adults consider a daily 10 microgram (mcg) vitamin D supplement during autumn and winter because the sun is not strong enough for the body to make it^[24].

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.