Is there a scientific reason that some people feel habitually cold?

Original Article Location:  Is there a scientific reason that some people feel habitually cold?
Author: Edyta Zielinska
Date: August 14, 2006

It’s true some people are always cold. They sleep under five comforters in the winter and always carry an extra sweater on the hottest summer days (hey, there’s always the risk of an over-zealous air conditioner!). Does this mean there’s something medically wrong with these people? Probably not—although there is a condition called severe cold intolerance, it’s rare and unlikely to be the problem.
Instead, some studies suggest that simply changing your lifestyle could help. Eating better, exercising more, and reducing stress are a few initial steps that could cut the cold.
The human body works in different ways to regulate temperature. For example, without moving at all, your muscles produce up to 25 percent of your body’s normal temperature. Muscles are always slightly contracted—a state called “muscle tone.” This partly explains the recommendation to exercise more: the more muscle mass you build, the more tone you have, and the more heat your body produces at rest. Internal organs, like your heart, liver, and kidneys are another major source of heat. They’re continuously working and, as a byproduct of that work, creating heat. The liver, for instance, is responsible for up to 20 percent of your body’s heat—so be good to your liver and put down that fifth beer!
All of this involuntary temperature regulation is orchestrated by the brain. Acting as an internal thermostat is one of the many jobs of the hypothalamus, an area at the base of the brain. When your body gets too hot, the hypothalamus turns on the AC—blood vessels near the surface of your skin open up to release the heat (sometimes making you flushed) and you start sweating. When your body gets too cold, the hypothalamus shuts off the AC and seals the windows. Small blood vessels close up to conserve heat, making your hands, nose and toes feel very cold. And if too much heat is lost, your brain tells your muscles to spasm into a shiver, upping the internal production of heat by increasing muscle tone.
But for the die-hard hypochondriac, that ever-present chill could potentially be a symptom of various syndromes and diseases. The two that would most likely warrant a check-in with the doctor are Raynaud’s disease and hypothyroidism.
Raynaud’s disease causes extremities, like fingers and toes, to turn blue in response to the cold or to emotional stress. This is usually accompanied by some pain or numbness in the hands, and when blood flow does return, the area usually gets red and tingles or throbs. It’s a rare disorder that affects more women than men. But if you think you have it, you may want to see a rheumatologist, since some cases develop into arthritic disease.
Another disorder that can cause cold intolerance is hypothyroidism, which happens when the thyroid gland does not produce enough of the hormones that control metabolism. Hypothyroidism can cause a person to gain weight, feel tired, sluggish or weak, and often also feel cold. Luckily, it can be diagnosed with a simple blood test, and medications to correct the problem are readily available.
So although most people’s sensitivity to the cold can be easily controlled with a few warmer articles of clothing, it’s always best to check with a doctor if you think it could be something more serious.

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