How is Body Temperature Controlled?
Maintaining a suitable body temperature is critical to humans. The various chemical reactions that our body relies on operate best when kept warm. It has been estimated, therefore, that up to 40% of the calories we consume are burned by the body as fuel to keep us warm.
A range of different processes operate to help keep our body temperature within reasonable boundaries. This process is known to scientists as “thermoregulation”. At its simplest we can think of two different systems; firstly there is how much heat we produce in the first place, and secondly there is how quickly heat is lost from the body.
Your body temperature, however, is not uniform, with some areas remaining much warmer than others. Studies show that while the temperature in your core may only vary by some 3’C this variance can be as much as 30’C in fingers and toes. Therefore getting cold hands is not in your imagination; they really can get a lot colder than other parts of your body.
Our body temperature is regulated by an area of the brain called the hypothalamus, which acts as a thermostat. When you get too hot, the hypothalamus dilates blood vessels near the surface of the skin to release heat, making your skin appear flushed and sweaty. When you’re cold, the hypothalamus constricts these blood vessels to conserve heat, making your hands and feet feel cold. If too much heat is lost, then muscles spasm (shiver) to produce heat.
The hypothalamus also controls the thyroid gland, which is largely responsible for the process of metabolism – and hence how much heat is produced by your body. When either the thyroid gland functions less efficiently, or when circulation is compromised, you may feel cold all the time.
If you find yourself constantly reaching for a jumper or blanket, here are some common factors that might be throwing off your internal temperature…
Low Iron Levels
Iron is a critical part of the blood. It helps red blood cells to carry oxygen around the body, ensuring each cell can function properly. Equally, iron deficiency can impact this process, and it is believed that this can lead to feeling cold all the time.
Studies seem to suggest that an iron deficiency affects thermoregulation in two different ways. Firstly, a lack of iron impacts the thyroid, making it less effective at generating the heat that your body needs. Alongside this, however, it also affects circulation. When your blood does not contain enough iron then it is harder for your cells to get the oxygen that they need. Blood flow can therefore increase to counteract this issue, but in doing so more warmth is lost as more hot blood flows near the surface of the skin.
A scientific study aimed to identify the relationship between iron levels and body temperature. They recruited women suffering from anaemia and then monitored their core body temperature when sat in a cold bath. The participants were then provided with an iron supplement in order to alleviate their anaemia, and the experiment was carried out again.
The women experienced considerable improvements in body temperature after supplementation when compared to the anaemic situation. As they summarised; “this experiment demonstrates a functional consequence of iron-deficiency anaemia in the balance of heat production and loss”.
Women of childbearing age are particularly prone to iron deficiency due to the monthly menstrual cycle and may find that feelings of coldness intensify each month with the loss of blood. Other symptoms to watch out for include pale skin, dizziness, extreme fatigue, and an irregular heartbeat.
Steps to Take
Increasing your iron intake is possibly one of the easiest potential treatments for feelings of cold. Iron supplements are an easy solution, while eating iron-rich foods such as lean meat, eggs, and leafy greens like spinach and kale are also beneficial. If you are experiencing any of the symptoms above, get your iron levels tested by a doctor.
Vitamin B12 Deficiency
Along with iron, vitamin B12 plays a crucial role in the production of red blood cells. Just the same, therefore, a deficiency may lead to persistent feelings of cold.
Steps to Take
Vitamin B12 is found primarily in animal-based foods, such as lean meat, fish and dairy. Most people can get all they need from diet alone, but if you avoid meat or dairy based products, you may benefit from a daily vitamin B12 supplement. A deficiency may also be caused by malabsorption, which means you struggle to absorb it from foods. If changes to your diet don’t help to relieve feelings of coldness, consult with your doctor.
If it’s just your hands and feet (the extremities) that feel cold, then you may well suffer from poor circulation, which isn’t necessarily anything to worry about. However, if the coldness is generally restricted to one side of your body, you may have a form of heart disease called atherosclerosis.
This occurs when the artery walls become clogged up with fatty substances, which results in less blood being pumped around to certain areas of the body.
Another cause of poor circulation is Raynaud’s disease, which affects around 10 million people in the UK, the majority of whom are women. Raynaud’s causes the blood vessels in the fingers, toes, ears, and nose to narrow in cold conditions, resulting in them turning blue. The muscles in blood vessel walls may also go into spasms, causing pain and numbness.
Steps to Take
It’s important to visit your doctor to determine the cause of poor circulation. While it is often completely harmless, heart disease or Raynaud’s disease require medical attention and can be treated with medication.
Studies also suggest that omega 3 oils may help to improve circulation, and so lessen feelings of cold. For example, in one study individuals with Raynaud’s were provided with fish oil capsules for a period of 12 weeks. Throughout the process, the volunteers were subjected to tests in cold conditions to measure how long it took to experience symptoms of the disease. They found that by the end of the test the participants taking fish oils increased the time it took to see symptoms in cold conditions from 31 minutes to an average of 46 minutes. It was therefore concluded that “ingestion of fish oil improves tolerance to cold exposure”.
Seasonal Affective Disorder (SAD)
It has been estimated that up to 20% of us may suffer from a degree of Seasonal Affective Disorder. It is a condition associated with feelings of depression, boredom or fatigue during the winter months. Scientists have noted that SAD sufferers tend to have lower levels of dopamine in their body, and that this is related to reduced light intensity during the winter.
Interestingly, thermoregulation is also very dopamine-dependent, so it has been proposed that people with Seasonal Affective Disorder may be more sensitive to cold weather, as their bodies are less effective at moderating internal temperatures.
This was tested experimentally in a group of volunteers, half of whom had been diagnosed with SAD while the others exhibited normal levels of dopamine. Participants in the study carried out exercise sessions in both the summer and the winter, with scientists monitoring changes in their body temperature.
Interestingly in the summer months no differences were observed in response to exercise. In contrast, as winter wore on the differences became more pronounced, and the SAD-affected individuals did not manage to control their body temperature as well.
Steps to Take
If you feel that you may be suffering from Seasonal Affective Disorder then it is crucial to seek advice from your doctor. The NHS also has some useful advice here.
To date, some of the most hopeful treatments have involved access to full-spectrum lights which mimic the sun’s rays, together with vitamin D supplementation. Combined these treatments seem to help improve the symptoms of SAD in many people, and as a result may help you to feel warmer.
Lack of Sleep
Studies have found that body temperature drops in those who don’t get a good night’s sleep. This is because sleep deprivation affects the nervous system and the regulatory mechanisms in the brain that regulates heat. The reduced activity in the hypothalamus area of the brain has a knock on effect on the body’s metabolism, causing it to become sluggish.
In a study participants were asked to place their hand into a cold water bath while having their body temperature monitored. They were then kept awake for the next 29 hours and were subjected to the same experiment. It was found that when sleep deprived the volunteers struggled to maintain a suitable body temperature, and they observed “vascular changes in the hand which impair the local cold tolerance”.
Steps to Take
Are you heroically trying to get by on just a few hours’ sleep each night? If so, you might just be contributing to feelings of cold all the time. Instead, take pleasure in achieving the recommended 7-9 hours of shut-eye per night. Natural sleep aids such as valerian or magnesium can also help to relax the body and promote restful sleep.
Additionally, if you spend your days sitting in front of a computer, there is a real need to stimulate your circulation. Using your muscles generates heat so exercise on a daily basis to keep the blood pumping and improve sleep at night.
Scientists have long noted that in cases where the thyroid gland is damaged or has to be removed the patient in question invariably suffers from reduced cold tolerance. It therefore follows that an underactive thyroid may lead to persistent feelings of cold – but how?
The hypothalamus instructs the thyroid gland to rev up or slow down metabolism. As a result, the thyroid is responsible for burning calories to generate heat and fuel. An underactive thyroid (hypothyroidism) doesn’t produce sufficient levels of the hormone thyroxine, which causes metabolism to slow and often leaves you feeling cold all over. Women are particularly at risk of an underactive thyroid.
Steps to Take
If you notice other symptoms of hypothyroidism such as thinning hair, brittle nails, extreme fatigue, irregular periods, or unexplained weight gain, it’s important to see a doctor. An underactive thyroid is often easy to treat with the right medication but it’s important to catch it early.
For milder cases supplements such as selenium are believed by many to have a positive impact.
Scientists used heat-sensing cameras to take snapshots of body temperature in both men and women. Their analysis showed that, on average, women tended to be 3’C colder than men.
There’s more. Another study found that while women generally cope with hot conditions better than men, they are less able to tolerate cold. They found that women generally have less capacity to produce heat through shivering, lose heat faster due to their smaller body size and that their circulatory system responds slightly differently to cold conditions.
It is believed that this is down to the oestrogen, which regulates blood flow to the peripheral blood vessels. High levels of the hormone can cause blood vessels to restrict even from a minimal amount of cold. As a result, blood flow to the skin, hands and feet shuts down sooner and more intensely than in men. While scientists are unsure why this natural process occurs, it may be that women are better programmed to maintain blood flow to their vital organs to support pregnancy.
Lastly, it is important to highlight that body temperature in women changes in response to the menstrual cycle. At ovulation the temperature rises, remaining there until menstruation, at which point women’s core body temperature drops back to the original level. This means that some women may feel colder at certain times than others.
Steps to Take
Boosting vitamin B levels, in particular B6, may help to balance oestrogen levels throughout the month and reduce extreme sensitivity to cold during the menstrual cycle. Good food sources include lean meat, whole grains, and eggs.
Many people stop exercising during the colder winter months but it’s important to keep physically active to keep the blood flowing. So layer up, put on a hat and gloves, and get moving.
If you have a low BMI of 18.5 or under you likely have a lack of body fat to insulate heat and keep you warm. People who are underweight also often lack muscle mass, which is important to maintain body temperature, speed up metabolism and produce heat. Without moving, the muscles produce up to 25% of your body’s natural temperature, so the more muscle you build, the more heat your body will produce at rest.
Steps to Take
Gradually increase weight by loading up on healthy foods rich in protein, good fats, and complex carbohydrates, and start strength training exercises to build muscle. Low weight can have different causes so it’s important to be properly diagnosed by a health professional, who will ensure the right care is in place.
If being underweight can make you feel cold all the time then surely being overweight will therefore help you to keep warm? After all, it makes sense that body fat can act as insulation, helping to retain body heat. Interestingly, however, a number of studies say this may not be the case…
Studies suggest, for example, that being overweight does indeed reduce heat loss around the abdomen, though in contrast heat loss through the hands and feet actually increases with body fat level.
Elsewhere, a group of overweight men were compared with men of normal body fat levels. They were all exposed to cold air for a period of an hour, before being allowed to warm back up. Body temperature was monitored throughout, and the results showed that the overweight men responded less effectively to getting cold.
Lastly, studies have suggested that obese patients tend to have a lower core body temperature than leaner individuals, which points to significant metabolic changes as body fat levels increase.
In short, don’t assume that just because someone is overweight that they feel less cold than their slimmer counterparts.
Steps to Take
Being overweight isn’t just a contributing factor to feeling cold all the time; it can also lead to all manner of other health conditions. Achieving a healthy body mass index (BMI) is therefore of great importance. A calorie-controlled diet combined with regular exercise will help to shift unwanted weight.
Some supplements may also be beneficial; caffeine may help to give your metabolism a “kick” while psyllium husk helps to make you feel full for longer, allowing you to lose weight without continual hunger pangs.
Doctors have noticed that people that have experienced significant injury in their hands tend to suffer from increased sensations of cold. For example a survey of patients that had suffered from fractures to the fingers or hands were asked to report on any problems with cold tolerance. It was found that 38% of patients reported severe problems. The experience is said to be close to 100% in those that have had fingers successfully reattached after injury.
Quite why this should occur is, as yet, unclear. Sadly, what is clear is that these symptoms tend to be long term. It may be that injury to the extremities in some way impacts the circulatory system, preventing the body from properly maintaining an optimum temperature.
Steps to Take
Sadly, no proven treatment is yet available. One scientific study on the phenomenon claims that “the exact cause of this problem is obscure, no specific treatment is available and little is known about the long-term prognosis”. If you have suffered a fracture to your feet or hands in recent years and now find yourself continually feeling cold the only real option is to follow the general guidelines for staying warm, such as wrapping up when you go outside and staying active throughout the day.
Muscles generate heat when they expand and contract. This is the very basis of shivering; tiny muscle spasms help to generate warmth. The bigger the muscles and more frequent the action, the greater the impact on body temperature. This means that sporting pursuits can help to warm up the body, while sitting still tends to have quite the opposite effect. Relaxing on the sofa at home, or jobs that entail sitting motionless at a desk for hours on end therefore can contribute to ongoing feelings of cold.
There’s more, however. It seems that exercise may have a longer-term impact on feelings of cold than those generated during and immediately after activity. Studies have found that people with active lifestyles – such as athletes – tend to be better at maintaining a suitable body temperature. One study investigated the impact of lifestyle on metabolic rate and found that “some lifestyle factors affect cold tolerance; in particular daily activity might improve our ability to control… heat production”.
Steps to Take
If you can’t remember the last time you visited the gym or worked up a sweat in the garden then it may be that your sedentary lifestyle is lowering your metabolic rate, making you feel cold all the time. Remedying this situation with regular exercise can help to reverse the trend.
Consider how you might manage to boost your weekly activity levels. Certainly intense exercise like workout classes or resistance training may help. For the rest of us, however, just wrapping up and heading out for a brisk walk or cycle ride may also offer long-term benefits when it comes to staying warm in the winter months.
Not Eating Enough
The heat that our body produces to keep us warm comes directly from our diet. As stated earlier, almost half of the calories most of us consume contribute to this process. It logically follows that going on a diet might impact thermoregulation, starving the body of the calories we need and therefore making us feel cold the entire time. But what does the science say?
A study recruited two categories of participants. One of these groups had been on a calorie-restricted diet for at least six years, while the other group consumed a normal western diet. Body temperatures of these individuals were monitored every minute for 24 hours to see how they responded to different conditions.
As hypothesised, the scientists found that the calorie-restricted group did indeed experience a lower average temperature both during both the day and the night when compared to the control group.
Steps to Take
Going on a diet can reduce your core body temperature, contributing to feelings of cold throughout the day. There are a number of possible solutions, however. The most obvious solution is to start eating more each day to “stoke” your metabolic rate.
Alongside this, however, what we eat and when we eat it also seem to have an impact on how warm we feel. Studies have shown, for example, that consuming the same number of calories divided up into a larger number of individual meals increases body temperature more than consuming all these calories at once.
The body also uses considerable energy warming up food that has been consumed before digestion. Moving from cold meals to warm ones not only frees up the energy that would otherwise have been used to heat it up but also helps to warm you up from the inside.
Every time you smoke, toxins from the cigarette enter the bloodstream. The most harmful of these is carbon monoxide, which irritates and damages the inner layer of blood vessel walls, allowing fats and plaque to stick to it. Nicotine also causes damage. This potent stimulant accelerates the heart rate by about twenty beats per minute, raises blood pressure, and constricts the blood vessels, reducing the amount of blood and oxygen circulating around the body. All of this increase the risk of blood clots forming and means that the heart has to work much, much harder.
Steps to Take
Take steps to quit smoking. There is lots of information available to help you quit and free support can be found on the NHS website. The good news is that once you stop, your health and circulation will improve.
Diabetes can result in circulatory problems, high blood pressure, and thyroid issues, all of which increase the risk of cold hands and feet. Constant exposure to elevated blood glucose levels can also damage blood vessel walls, increasing the risk of fatty plaque build-ups. Over time, diabetes can lead to nerve damage (peripheral nephropathy), which causes numbness and pain in the hands and feet.
Steps to Take
In addition to poor circulation, other symptoms to look out for include increased thirst, nausea and vomiting, loss of appetite, shortness of breath, and swelling in the face, feet or hands. If you notice the symptoms, visit your doctor. If you have already been diagnosed with diabetes, make sure you have an annual foot examination to test the circulation in your feet.