Bone Marrow Fat

It surprises a lot of people to know this, but your skeleton hides a secret: It is full of fat!

In fact, bone marrow fat cells comprise the largest population of cells in the bone marrow cavity and is the third largest fat depot, after subcutaneous fat (under the skin) and visceral fat (stored in a person’s abdominal cavity and also known as “active fat” because it influences how hormones function in the body).

Over a century ago, scientists first noticed that our bone marrow (spongy tissue inside the bones) contains fat-storing cells called 𝑎𝑑𝑖𝑝𝑜𝑐𝑦𝑡𝑒𝑠. Having adipocytes in our bones might strike you as unusual, but it isn’t. Bone marrow adipose (fat) tissue develops steadily after birth and accumulates rapidly during puberty such that, by the time we reach adulthood, it can comprise up to 70% of bone marrow volume. This represents over 8% of total fat mass!

Increased bone marrow fat is associated with lower bone mineral density and increased skeletal fragility — such as in osteoporosis, ageing and estrogen deficiency — which, of course, can lead to increased risk of fractures and breaks, more diagnostic procedures, and radiation, as well as to more surgeries.

This is why obesity is an important risk factor for osteoarthritis sufferers.

High amounts of fat around the liver, muscle tissues and in the blood is more likely to cause osteoporosis because when internal organs are engulfed in fat there’s also fat inside the bone marrow.

This affects the marrow’s ability to produce 𝑜𝑠𝑡𝑒𝑜𝑏𝑙𝑎𝑠𝑡𝑠 — specialized cells that are in charge of bone formation.

In time, the obese person’s bones grow weaker; more likely to fracture when traumatized.

Bone marrow fat acts as a metabolically active organ and plays an active role in energy storage, endocrine function, bone metabolism, and the bone metastasis of tumors.

Men have higher bone marrow fat than women, but it increases with aging for both sexes and with menopause.   

Here you can see what fat looks like in the spine. And when it comes to the spine specifically, remember: Since bone marrow fat makes bones weak, a spine filled with fat is not as strong as one without!