Hair loss is one of the most emotionally distressing health changes a person can experience. It is also one of the most frequently dismissed. Go to your GP with hair thinning and you're likely to be told it's stress, or hormones, or just something that happens as you get older. You might be offered a basic blood test. It comes back normal. And you're left with no answers and continuing hair loss.
The problem is not that there's nothing wrong. The problem is that the standard blood test isn't looking at the right things.
In the majority of cases of non-genetic hair thinning and hair loss — particularly in women — there is an identifiable, treatable underlying cause. It can be found in a blood test. And it can be addressed. But only if you're testing the right markers.
Why hair loss happens — the physiology
Each hair follicle goes through a continuous cycle of growth, rest, and shedding. At any given time, around 85–90% of your hair follicles are in the active growth phase (anagen), with the remainder resting or shedding. This cycle is exquisitely sensitive to your internal environment — your nutrient status, hormone levels, inflammatory load, and thyroid function all directly regulate how long follicles spend in the growth phase and how effectively they produce hair.
When something disrupts this environment — a nutrient deficiency, a hormonal shift, a period of acute stress, a thyroid problem — the follicles respond by shortening the growth phase and moving more hair into the shedding phase simultaneously. The result is the kind of diffuse, all-over thinning that most people with non-genetic hair loss experience — often appearing as increased shedding in the shower, more hair on the pillow, and a gradually widening parting.
This type of hair loss — called telogen effluvium — is almost always caused by something systemic. And systemic causes have systemic solutions.
The blood tests that reveal why your hair is thinning
Ferritin — the most important marker you've probably never had tested
Ferritin is your body's stored iron — the reserve your cells draw on when immediate iron supply is insufficient. It is the single most important blood marker for hair health, and it is the one most frequently missed on standard NHS testing, which typically only measures serum iron or haemoglobin.
Hair follicles are among the most metabolically active structures in your body. They require a significant and consistent supply of iron to remain in the active growth phase. When ferritin drops — even while haemoglobin remains normal — follicles are among the first structures to feel the shortage. They respond by shortening the growth phase and moving into resting mode, resulting in increased shedding two to four months after the ferritin drop occurred.
This delayed onset is one of the reasons ferritin-related hair loss is so confusing — by the time the shedding appears, the deficiency that caused it is already weeks or months old. Many women in their 30s and 40s — particularly those with heavy periods, who have been pregnant, or who follow plant-based diets — have chronically low ferritin without ever knowing it. Their haemoglobin is normal. Their GP tells them their bloods are fine. Their hair keeps falling out.
Optimal ferritin for hair health is generally considered to be above 70 μg/L — significantly higher than the reference range lower limit of around 12–15 μg/L that many labs use. A result of 20 μg/L is technically within range and will be reported as normal. For your hair follicles, it isn't.
Thyroid function — TSH, Free T4, Free T3, and antibodies
Thyroid dysfunction is one of the most common causes of diffuse hair thinning in women and is significantly underdiagnosed. Both hypothyroidism and hyperthyroidism cause hair loss — in different ways and through different mechanisms, but both disrupt the follicle growth cycle.
In hypothyroidism, reduced metabolic activity slows follicle cell turnover and extends the resting phase. In hyperthyroidism, accelerated metabolism disrupts the follicle cycle in the opposite direction. Autoimmune thyroid conditions — particularly Hashimoto's thyroiditis — are closely associated with a specific type of hair loss called alopecia areata, characterised by patchy rather than diffuse loss.
A standard NHS thyroid test checks TSH only. This is insufficient. Free T3, Free T4, and thyroid antibodies are all necessary to get a complete picture — and it's only with the complete picture that thyroid-related hair loss can be properly identified and addressed.
Hormones — androgens, oestrogen, progesterone, and DHEA
Hormonal causes of hair loss are among the most common and most frequently overlooked. Androgenetic alopecia — the hair loss pattern driven by sensitivity to dihydrotestosterone (DHT), a derivative of testosterone — affects women as well as men, though it presents differently. In women it typically causes diffuse thinning across the top of the scalp rather than the receding hairline pattern seen in men.
Elevated androgens — testosterone and DHEA — drive DHT production and accelerate androgenetic hair loss. Polycystic ovary syndrome (PCOS), which involves elevated androgens, is one of the most common causes of hair loss in women of reproductive age.
The sharp drop in oestrogen and progesterone that occurs in perimenopause and menopause removes the protective effect these hormones have on hair follicles, often triggering significant hair thinning. Many women first notice meaningful hair loss in their late 40s and early 50s — and the cause is hormonal rather than genetic or nutritional.
A full hormone panel including testosterone, free testosterone, DHEA-S, oestradiol, progesterone, and sex hormone binding globulin (SHBG) gives a comprehensive picture of the hormonal environment your hair follicles are operating in.
Vitamin D
Vitamin D receptors are present in hair follicle cells, and vitamin D plays a direct role in the follicle cycle — particularly in the transition from resting phase back into active growth. Low vitamin D is associated with increased shedding and slower regrowth, and is significantly more common in people with alopecia areata than in the general population.
Given that the majority of UK adults are deficient in vitamin D for much of the year, testing and optimising vitamin D levels is a straightforward and frequently impactful intervention for hair health.
Zinc
Zinc is essential for protein synthesis, cell division, and the function of the oil glands surrounding each hair follicle. Deficiency impairs hair follicle cycling and is associated with both diffuse hair thinning and structural changes to the hair shaft — hair that appears thinner, more brittle, and lacking in lustre. Zinc deficiency is more common than most people realise, particularly in people following plant-based diets or with gut absorption issues.
B12 and folate
B12 and folate are essential for the rapid cell division that hair follicle growth requires. Both deficiencies are associated with diffuse hair shedding and are particularly common in people following vegan or vegetarian diets, those over 40, and anyone with gut absorption issues. Testing both total and active B12 alongside folate gives a complete picture.
Inflammatory markers and autoimmune screening
In cases of patchy hair loss or alopecia areata, autoimmune factors are frequently involved. Thyroid antibodies, ANA (antinuclear antibody), and inflammatory markers including CRP can help identify an autoimmune component that changes the management approach significantly.
What happens after your results
A comprehensive hair loss blood panel gives you specific, actionable information — not a vague reassurance that everything is normal. At Boost & Glow, Lucy will walk you through your results in detail, explaining which markers are below optimal for hair health and what the likely contribution of each finding is to your hair loss.
From there, the plan is built around your specific results. Iron deficiency is addressed through supplementation at therapeutic doses — not the generic low-dose iron tablets available over the counter. Thyroid dysfunction is discussed in the context of appropriate next steps, whether that's GP referral for medication or nutritional support for thyroid function. Hormonal imbalances are addressed through targeted interventions appropriate to your specific hormonal picture.
IV vitamin therapy plays a valuable supporting role in hair loss recovery. For patients with significant nutrient deficiencies — particularly iron, B12, and zinc — IV delivery bypasses the gut and ensures therapeutic concentrations reach the follicles regardless of absorption issues. High-dose IV vitamin C supports collagen synthesis in the scalp and follicle structure. Regular IV therapy as part of a hair loss recovery protocol delivers sustained nutrient support that oral supplementation often cannot replicate.
Sam's nutrition planning service builds a dietary foundation that actively supports hair health — ensuring adequate protein intake for keratin production, optimising the specific micronutrients most critical for follicle function, and addressing any dietary patterns contributing to the deficiencies identified in your blood test.
Who should get a hair loss blood test?
If you are experiencing diffuse hair thinning or increased shedding, you have noticed your parting widening or your ponytail getting thinner, you are losing hair in patches, your hair has changed in texture — becoming finer, more brittle, or duller — or your hair is growing more slowly than it used to, a blood test is the logical first step. Before spending money on topical treatments, hair supplements, or clinical procedures, understanding the internal causes of your hair loss gives you the information to make genuinely effective choices.
At Boost & Glow
Lucy carries out all blood testing using venous draws at our clinic in Epping or at your home across Essex, Hertfordshire, and London. A comprehensive hair loss panel covers ferritin, full iron studies, full thyroid panel including antibodies, full hormone panel, vitamin D, zinc, B12, folate, and inflammatory markers — giving you the most complete picture available of why your hair is changing and what to do about it.
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