IGF-1

Insulin-like growth factor — a hormone driving tissue growth

IGF-1 is insulin-like growth factor 1, the main pathway through which growth hormone acts. It stimulates tissue growth, supports muscle and bone, and reflects the workings of the "pituitary → liver" axis.

Because the IGF-1 level is more stable than the fluctuating growth hormone, it is IGF-1 that is used to assess this system. IGF-1 has a "flip side" too: in the biology of aging its high activity is linked to accelerated growth, and a moderately low level to longevity.

Reference ranges

The normal range depends strongly on age and falls over time (ng/mL):

25 – 39 years	≈ 114 – 400
40 – 54 years	≈ 90 – 360
Over 54 years	≈ 70 – 290
Always assessed by age	the ranges differ for children and adults

Important: IGF-1 naturally falls with age. So the result is interpreted strictly against the age-specific range, not a single range.

What an elevated level means

A high IGF-1 in adults most often points to an excess of growth hormone. Its classic cause is acromegaly (usually from a pituitary adenoma): the hands, feet and facial features enlarge, and the risk of diabetes and heart disease rises.

From a longevity standpoint, chronically high activity of the IGF-1 axis is linked to accelerated aging and risks, so "revving it up" without indications is not recommended.

What a low level means

A low IGF-1 in adults means a lack of growth hormone or of its action.

Causes: growth hormone deficiency (pituitary disease), severe undernutrition and malabsorption, liver disease (where IGF-1 is synthesized), poorly controlled diabetes, aging. A marked deficiency in adults shows itself as loss of muscle, weakness and reduced quality of life.

How the test is done

IGF-1 is measured in blood from a vein; it is relatively stable through the day, so there are no strict timing restrictions. The result is always compared with the age-specific range.

When an excess or deficiency of growth hormone is suspected, IGF-1 is supplemented with special tests (for example, a challenge test) performed by an endocrinologist.

What affects the value

Growth hormone — the main regulator of the IGF-1 level.
Age — IGF-1 falls over the years.
Nutrition and protein — undernutrition lowers the level.
Liver disease — reduces synthesis.
Poorly controlled diabetes — lowers it.
Sex and puberty — affect it (a peak in youth).

Frequently asked questions

What does IGF-1 show?

The workings of the growth hormone axis. Growth hormone is released in pulses and changes quickly, whereas IGF-1 is stable and reflects its overall action. So it is IGF-1 that is used to assess an excess (acromegaly) or deficiency of growth hormone.

Why is the IGF-1 range read by age?

The IGF-1 level peaks in youth and naturally falls with age. So there is no single range: the same result can be normal for an older person and too low for a young one. It is assessed strictly against the age-specific range.

How is IGF-1 linked to longevity?

In the biology of aging, moderately reduced activity of the growth hormone / IGF-1 axis is linked to a longer lifespan in a number of models and in people, whereas its excessive stimulation is linked to accelerated growth and risks. So "raising" IGF-1 without medical indications is not recommended.

Sources

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This content is educational and does not replace consultation with a physician. Reference ranges may vary depending on the laboratory and method — rely on the ranges stated on your own test report.

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