by Esther Crain

Feeling chilly when the AC is blasting is one thing. But if you're always shivering, or your hands and feet feel like blocks of ice while everyone else nearby says the temperature feels toasty, then it's time to investigate. It's common for women to report feeling cold, partly as a result of physiology and also a greater susceptibility to conditions that can contribute to coldness, says Holly Phillips, MD, medical contributor for CBS2 News and author of The Exhaustion Breakthrough. This checklist of 10 reasons your internal thermostat is out of whack can help you get a handle on why you're chronically freezing your butt off.

You're too thin

Low body weight—defined as a BMI hovering around 18.5 or under—can chill you out for a couple of reasons. First, when you're underweight, you lack an adequate level of body fat to insulate you from cold temperatures, explains Maggie Moon, RD, a Los Angeles–based nutritionist. The other thing is, to maintain that low BMI, you have to reduce your food intake so you likely aren't eating very much at all. Skimping on calories puts the brakes on your metabolism, so you don't create enough body heat. Consider putting on a few pounds by loading up on whole, healthy foods that contain lots of protein, fat, and complex carbohydrates.

Your thyroid is out of whack

Add cold intolerance to the long list of health issues you can blame on the butterfly-shaped gland in your neck. "Always being cold is a telltale sign of hypothyroidism, which means your thyroid doesn't secrete enough thyroid hormone,” says Dr. Phillips. Without the right level of this hormone, your metabolism slows, preventing your body's engine from producing adequate heat. Other signs of hypothyroidism are thinning hair, dry skin, and fatigue.

Approximately 4.5% of Americans have this condition, and rates are higher in women who have recently been pregnant or are over age 60. If you suspect a thyroid problem, see your doctor, who can confirm the diagnosis with a blood test and get your thyroid out of the slow lane with prescription meds.

You don't get enough iron

Low iron levels are one of the most common reasons for chronic coldness. Here's why: Iron is a key mineral that helps your red blood cells carry oxygen throughout your body, bringing heat and other nutrients to every cell in your system, explains Dr. Phillips. Without enough iron, red blood cells can't effectively do their job, and you shiver.

Iron is also crucial because a deficiency can make your thyroid lethargic, leading to hypothyroidism, which further leaves you freezing, says Moon. Iron supplements can help, but the best way to boost your iron intake is through healthy food: meat, eggs, leafy greens like spinach, and seafood are the best options, says Moon.

You have poor circulation

If your hands and feet are always like ice but the rest of your body feels comfortable, then a circulation problem that keeps blood from flowing to your extremities might be to blame. Cardiovascular disease can be one cause; it's a sign that your heart is not pumping blood effectively, or a blockage of the arteries prevents blood from getting to your fingers and toes, explains Margarita Rohr, MD, internist at NYU Langone Medical Center in New York City. Smoking can also bring on circulation issues, since lighting up constricts blood vessels, says Dr. Phillips.

Another possibility is a condition called Raynaud's disease, which prompts blood vessels in your hands and feet to temporarily narrow when your body senses cold, says Rohr. Reynaud's disease can be treated with meds, but you need to check in with your doctor for a diagnosis first.

You don't get enough sleep

"Sleep deprivation can wreck havoc on your nervous system, throwing off regulatory mechanisms in the brain that affect body temperature,” says Dr. Phillips. It's not clear why this happens; studies suggest that in response to the stress of not getting quality snooze time, there's a reduction in activity in the hypothalamus, the control panel of the brain where body temperature is regulated. A study from theEuropean Journal of Applied Physiology appears to back this up: researchers documented a drop in body temperature in 20 sleep-deprived young adults. Metabolism may be a culprit here as well. When you're fatigued from a restless night, your metabolism works at a more sluggish pace, says Dr. Phillips, producing less heat and slower circulation. 

You're dehydrated

"Up to 60% of the adult human body is water, and water helps regulate body temperature,” says Moon. "If you're adequately hydrated, water will trap heat and release it slowly, keeping your body temperature in a comfortable zone. With less water, your body is more sensitive to extreme temperatures.” Water warms you up another way as well. It helps power your metabolism, and a sluggish metabolism translates into less overall body heat. Aim for the requisite eight glasses a day at a minimum, recommends Moon, but always drink more before and after workouts.

You don't consume enough vitamin B12

This nutrient found only in animal products plays big role in preventing big chills. "The body needs vitamin B12 to make red blood cells, which carry oxygen through your system,” says Moon. "Not having enough can lead to B12-deficiency anemia, or a low red blood cell count, resulting in chronic coldness.” Vitamin B12 deficiencycan be caused by a poor diet, so aim to get more lean meat, fish, and dairy into your meals. But sometimes low levels are triggered by an absorption issue. If your diet is high in B12 but you shiver all the time, check in with your doctor for a vitamin B12 test.

You're a woman

Find yourself in a constant battle with your spouse or male officemates for control of the thermostat? Turns out that feeling cold really is a gendered condition. "In general, women are better at conserving heat than men,” says Dr. Rohr. "In order to do this, women's bodies are programmed to maintain blood flow to vital organs such as the brain and heart.” This directs blood flow toward these organs and away from less vital organs like hands and feet, says Dr. Rohr, which leaves these body parts chronically cold. Science bears this out: a University of Utah study found that though women had a slightly higher core body temperature than men, their hands came in at an average of 2.8 degrees cooler.

You have diabetes

Diabetes that's not kept in check can lead to a condition called peripheral nephropathy, a constant attack on the nerves that provide sensation to your hands and feet, says Dr. Rohr. "When this develops, you experience numbness and sometimes pain in the hands and feet, and since these nerves are also responsible for sending message to the brain regarding temperature sensation, your hands and feet may feel cold,” she says. Diabetic nephropathy develops gradually, so you may not realize you have it. But if you are diabetic or have symptoms of the disease (frequent urination, feeling tired, and having increased thirst are three classic signs) see your doctor.

You need to bulk up your muscle mass

Muscle helps maintain body temperature by producing heat, says Dr. Rohr, so not having enough muscle tone contributes to feeling frosty. Also, having more muscle mass fires up your metabolism, which fights the perma-freeze feeling. Hitting the weight room at the gym or investing in free weights will help build the muscle that powers your furnace and functions like an internal blanket so you can throw off that wool one wrapped around your shivering shoulders.