Does the cold really ‘seep into your bones’?

Another cold snap is approaching. Some people deal with it by taking an invigorating walk outside, while others hibernate with a cozy blanket and biscuits.

But one thing seems to be common when temperatures drop: we like talking about how cold it feels. Comments such as “I am so cold, I can feel it in my bones” are a common greeting in wintertime.

So, is there any truth to this particular complaint?

In the UK, the relatively high humidity even in cold temperatures means moisture in the air moves the warm air next to our bodies away quite quickly. It also sees moisture absorbed into our clothes, which then conducts heat away from the body. Water has an almost 70-fold higher rate of heat transfer than air.

The body is most efficient at approximately 37°C, but our extremities can be up to 6°C cooler. And there are variations around this body temperature dependant on sex, age and health status. Older people tend to feel the cold more, and women are more sensitive to the cold than men.

How cold affects our bones

Our bones don’t actually feel the cold as we sense it. They lack the same temperature-sensitive receptors that we have in our skin. There is a good reason for this, given our major bones are buried under layers of muscles, connective tissue and skin, so temperature sensing isn’t really key for them.

However, just because bones don’t “feel” the cold, it doesn’t mean the cold doesn’t have an affect on them. They can sense temperature change, particularly cooling, from nerves in the outermost lining of bone, known as the periosteum. This layer has what many scientists view as a net of neurons (cells that transmit signals) arranged in a fishnet-like pattern that senses distortion or injury of the underlying layers of bone.

Although short-term exposure of the body to the cold isn’t a problem for bones, prolonged exposure over a number of weeks can shorten their length, reduce their thickness, and decrease bone mineral density.

Other musculoskeletal tissues are much more susceptible to the changes in temperature and pressure. Synovial fluid, the lubricant of most major joints, becomes thicker when temperatures decline. This makes it harder and more uncomfortable for joints to move normally, which is exacerbated in people with underlying joint conditions such as rheumatoid or osteoarthritis.

The cold also causes contraction of tissues, making things tighter and stiffer. Tendons, which connect muscles to bone, increase in stiffness. Ligaments, which attach different bones around joints, also become stiffer.

Both of these changes make it harder for muscles to exert their action to move bones, requiring more force and decreasing their range of motion. This is exacerbated with humidity, which is common in the UK all year round.

These effects happen in tandem with reduced blood flow to our extremities. This protective mechanism is designed to ensure our core, where all our critical major organs are, doesn’t drop from the optimum operating temperature of 37°C. Reduced blood in these tissues also contributes to the tissue contraction, as less blood is entering them.

All of these changes result in an increase in mechanical strain or pressure upon receptor cells in the bones and surrounding tissues. This can trigger pain receptors, which may be perceived as cold.

The brain also plays a role. In the UK, grey skies often accompany the cold and damp. London averages 3.4 hours of sunshine in December, for example, while the US state of Colorado averages around eight hours of sunlight in the same month.

These dark winter months in the northern hemisphere mean many of us don’t get sufficient sunlight to synthesise enough vitamin D. You may know vitamin D deficiency is associated with poor bone health and conditions such as rickets (in children) and osteomalacia (adults). But it also has other implications in how cold feels.

Research suggests that people with low vitamin D levels have increased sensitivity to pain, particularly musculoskeletal pain.

This isn’t the only nervous-system effect that vitamin D has on cold perception. It is also linked with increased anxiety and depression symptoms. People with these conditions have altered tolerance when it comes to temperature.

Sunlight exposes the skin to the Sun’s radiation and visible light, both of which have a natural warming effect. So sunny and dry cold feels very different to damp, grey cold.

The good news is that taking on extra calories can help you ride out the latest cold snap. Wearing lots of layers and moving around as much as possible will also help keep you warm, by generating and trapping as much heat as possible against the body.

Adam Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.