Cold climates change what your body needs in a few predictable ways. Staying warm, wearing heavy clothing and moving through snow all burn extra energy, so active people outdoors in the cold often need more calories than usual. Thirst is weaker in the cold, winter sun at high latitudes makes little or no vitamin D, and iron and regular warm meals help you keep up with the demands.
Key Takeaways
- Cold exposure raises energy needs through shivering, heavy winter clothing, breathing cold air and hard work in snow; field studies of soldiers in the cold measured roughly 4,600 to 4,900 calories a day.
- People in the cold often eat less than they burn, even when food is available, so plan regular meals and snacks.
- Cold can blunt thirst by up to 40% in lab studies, so drink on a schedule rather than waiting until you feel thirsty.
- Above roughly 42 degrees north, winter sunlight produces little or no vitamin D for several months; adults need 15 to 20 mcg (600 to 800 IU) a day from food or supplements.
- Iron carries oxygen in the blood; women aged 19 to 50 need 18 mg a day and men need 8 mg.
Evidence grade: Moderate. Energy and fluid findings come from consistent but small field and laboratory studies, mostly in military personnel; vitamin D and iron amounts are established NIH reference values.
Cold-Climate Nutrition at a Glance
| Need | What changes in the cold | What to do |
|---|---|---|
| Energy (calories) | Shivering, heavy clothing, cold air and snow travel raise energy use [5][7] | Eat regular meals plus calorie-dense snacks when you are active outdoors |
| Fats | Fat supplies 9 calories per gram, more than twice carbohydrate or protein [12] | Include oily fish, nuts, seeds, olive or canola oil and avocado |
| Fluids | Thirst drops by up to 40% in the cold [8] | Drink on a schedule; warm drinks and soups count |
| Vitamin D | Little or no skin production from winter sun at higher latitudes [10] | 15 mcg (600 IU) a day for adults up to 70; 20 mcg (800 IU) over 70 [1] |
| Iron | Needed to carry oxygen; low iron was linked to poorer heat regulation in one small study [2][11] | 8 mg a day for men and women over 50; 18 mg for women 19 to 50 [2] |
Why Cold Weather Changes Your Nutrition Needs
Your body has two main ways to defend its core temperature in the cold. Blood vessels in the skin narrow to reduce heat loss, and shivering produces extra heat by burning more fuel [7]. Both are useful, but shivering costs energy.
A 2024 review from the U.S. Army Research Institute of Environmental Medicine listed several other reasons that work in the cold costs more energy: heavy winter clothing and boots, breathing cold air, bad weather, and cold-specific tasks such as walking through snow or pulling loads. Wind, wet conditions and altitude add to the strain [5]. The same review warned that the high energy cost raises the risk of running a calorie deficit and becoming dehydrated, both of which can reduce physical and mental performance [5].
A 2020 review reached a similar conclusion: environmental extremes, including cold, can raise energy expenditure and speed up the loss of body water and muscle protein, so standard guidelines may fall short for long, hard work in those settings [6].
How Many Extra Calories? What Military and Arctic Research Shows
Most of the best measurements come from soldiers, because armies need to know how much food to carry. A 2005 summary of studies in 424 male military personnel found average energy use of about 4,610 calories a day, ranging from about 3,100 to 7,100 calories depending on the unit and mission. Women averaged about 2,850 calories a day. Compared with temperate conditions, energy use tended to be higher in the cold or at high altitude [3].
A 2020 study of 10 Canadian Armed Forces reservists on a winter training course measured energy use with doubly labelled water, the gold-standard method. They burned about 4,917 calories a day but ate only about 2,377, even though their rations provided about 5,685 calories. They lost 2.7% of their body weight during the course [4]. The researchers described this as voluntary under-eating.
These numbers come from hard physical work in extreme conditions. Someone who walks to the car and works indoors all winter does not need 5,000 calories. The practical lessons still apply to skiers, winter hikers, outdoor workers and anyone spending long hours in the cold:
- Your needs rise with time outdoors, activity level and the weight of your gear.
- Appetite does not reliably keep up, so eat on a plan rather than by hunger alone.
- Carry food that is easy to eat with gloves on and that will not freeze solid.
Our guide to high-calorie foods for cold weather lists practical options.
Fats, Carbohydrates and Protein in Winter
When you need more energy in a small volume of food, fat is the most efficient source. It provides 9 calories per gram, compared with 4 calories per gram for carbohydrate and protein. Fat also helps your body absorb vitamins A, D, E and K [12].
Choose mostly unsaturated fats, such as olive and canola oil, nuts, seeds, avocado and oily fish [12]. Oily fish such as trout and salmon also supply vitamin D, which matters in winter (see below) [1].
Carbohydrates and protein still belong on the plate. Whole grains, potatoes, beans, dairy, eggs, fish and meat fill out a cold-weather diet, and the 2020 review notes that hard work in extreme environments can speed up muscle protein loss when energy intake falls short [6].
Hydration: Thirst Is Less Reliable in the Cold
Dehydration is easy to overlook in winter because you do not feel hot or sweaty. In a 2004 laboratory study, men who walked or stood in 4°C (39°F) air felt up to 40% less thirsty than in warm air. That happened whether they started out well hydrated or already dehydrated [8]. The studies were small (eight and nine men), but they show why thirst is a poor guide in the cold.
In the field, the problem is often access. U.S. Army cold-weather feeding studies found that rations and water freeze, and that people need deliberate planning to drink and eat enough to avoid weight loss and dehydration [9].
- Drink at regular times, such as with each meal and every break.
- Use insulated bottles so water does not freeze.
- Count warm drinks, soups and stews toward your fluid intake.
For more on fluids and activity, see hydration and its role in recovery.
Vitamin D at High Latitudes
Your skin makes vitamin D when it absorbs ultraviolet B (UVB) light from the sun. How much you make depends on the season, time of day, length of day, cloud cover, skin pigment and age. UVB does not pass through window glass, so sunshine through a window does not count [1].
Latitude matters a great deal. A classic 1988 study exposed skin samples to sunlight on clear days. In Boston (42.2°N), winter sun produced no previtamin D from November through February. In Edmonton, Canada (52°N), that "vitamin D winter" ran from October through March. Farther south, at 34°N and 18°N, skin still made vitamin D in midwinter [10].
The NIH sets the Recommended Dietary Allowance (RDA) at 15 mcg (600 IU) a day for people aged 1 to 70 and 20 mcg (800 IU) for adults over 70. These values already assume minimal sun exposure [1]. Yet Americans average only about 5.1 mcg (204 IU) a day from foods and drinks [1]. Good food sources include [1]:
- Rainbow trout, farmed and cooked, 3 ounces: 16.2 mcg (645 IU)
- Sockeye salmon, cooked, 3 ounces: 14.2 mcg (570 IU)
- White mushrooms exposed to UV light, ½ cup: 9.2 mcg (366 IU)
- Vitamin D-fortified 2% milk, 1 cup: 2.9 mcg (120 IU)
If you live far from the equator and rarely eat fatty fish, a supplement is a common way to reach the RDA. Our vitamin D3 and K2 guide explains forms, doses and testing.
OPA Women's Daily Multivitamin lists 10 mcg of vitamin D3 per two-capsule serving, which is two-thirds of the 15 mcg adult RDA, along with B vitamins (including B12 and folate), 150 mg of vitamin C, 15 mg of zinc and 50 mg of magnesium. It does not list iron among its key ingredients, so it does not cover the iron needs discussed below. Food, sunlight in summer and any other supplements you take all add to your vitamin D total.
Iron and Staying Warm
Iron is part of hemoglobin, the protein in red blood cells that carries oxygen from your lungs to your tissues. It is also part of myoglobin, which supplies oxygen to muscle [2]. Adults need [2]:
- 8 mg a day for men and for women over 50
- 18 mg a day for women aged 19 to 50
Iron status may also affect how well you handle the cold. In a small 1990 study, women with iron-deficiency anemia kept a lower core temperature than women with normal iron during 100 minutes in a cool water bath. Women with low iron stores but no anemia responded like the control group. After iron supplementation, the temperature response of the anemic women improved [11]. This was one small study, and it does not mean extra iron warms people who already have enough.
Meat, poultry and seafood provide heme iron, which is well absorbed. Beans, nuts, vegetables and fortified grains provide nonheme iron. Eating vitamin C-rich foods or some meat or fish at the same meal helps you absorb more nonheme iron [2]. For more, read the role of iron in energy levels.
Warm Meals, Regular Snacks and Comfort Foods
The research on cold-weather eating keeps returning to one point: people tend to eat and drink less than they need, even when food is available [4][9]. Warm meals help in practical ways. Food that is hot and ready is more likely to get eaten, and soups and stews add fluid at the same time.
- Plan a hot breakfast and dinner on cold days, such as oatmeal with nuts, eggs, chili, lentil soup or a fish stew.
- Pack snacks you can eat on the move, such as nuts, trail mix, cheese, nut butter sandwiches and dried fruit.
- Enjoy comfort foods, but build most meals around whole foods, so the extra calories also bring protein, fiber, vitamins and minerals.
Safety and Interactions
- Vitamin D. The upper limit for adults is 100 mcg (4,000 IU) a day from all sources unless a clinician advises otherwise [1]. Talk to your doctor or pharmacist about vitamin D if you take orlistat, a statin such as atorvastatin, lovastatin or simvastatin, a corticosteroid such as prednisone, or a thiazide diuretic [1].
- Iron. Do not take iron supplements unless you need them. Doses of 45 mg a day or more can cause nausea and constipation [2]. Talk to your doctor or pharmacist about iron if you take levodopa, levothyroxine (which should be taken 4 hours apart from iron) or a proton pump inhibitor such as omeprazole [2].
- Calories. The very high intakes in military studies reflect extreme workloads. If you are not doing that kind of work, extra calories will simply add weight.
- Medical conditions. If you have a heart, lung or circulation condition, or you follow a fluid or diet plan from your clinician, ask how cold-weather activity should change your eating and drinking.
Frequently Asked Questions
How many more calories do I need in cold weather?
It depends on how much time you spend outside and how hard you work. Soldiers training in the cold have burned roughly 4,600 to 4,900 calories a day [3][4], but most people who spend winter mainly indoors need little extra. If you ski, hike or work outdoors for hours, eat regular meals plus calorie-dense snacks, and watch for unplanned weight loss.
Do I need to drink as much water in winter?
Yes. Cold can reduce your sense of thirst by up to 40% [8], so you may need more fluid than you feel like drinking, especially when active. Drink at set times and count warm drinks and soups.
Can I make vitamin D from winter sunlight?
At higher latitudes, usually not. Winter sun produced no vitamin D in skin samples in Boston from November through February, or in Edmonton from October through March [10]. Food and supplements fill the gap; adults up to 70 need 15 mcg (600 IU) a day [1].
What are good fat sources for the winter season?
Oily fish such as salmon and trout, nuts, seeds, avocado, and olive or canola oil. They are calorie-dense, help you absorb fat-soluble vitamins, and fish adds vitamin D [1][12].
Does iron help you stay warm?
Iron carries oxygen in your blood. One small study found that women with iron-deficiency anemia held their body temperature less well in a cool bath until their iron was restored [11]. If your iron is already adequate, extra iron is not expected to make you warmer.
Sources
- NIH Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. Updated 2025.
- NIH Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals. Updated 2025.
- Tharion WJ, Lieberman HR, Montain SJ, et al. Energy requirements of military personnel. Appetite. 2005.
- Ahmed M, Mandic I, Desilets E, et al. Energy Balance of Canadian Armed Forces Personnel during an Arctic-Like Field Training Exercise. Nutrients. 2020.
- Schafer EA, Chapman CL, Castellani JW, Looney DP. Energy expenditure during physical work in cold environments: physiology and performance considerations for military service members. J Appl Physiol. 2024.
- Pasiakos SM. Nutritional Requirements for Sustaining Health and Performance During Exposure to Extreme Environments. Annu Rev Nutr. 2020.
- Castellani JW, Young AJ. Human physiological responses to cold exposure: Acute responses and acclimatization to prolonged exposure. Auton Neurosci. 2016.
- Kenefick RW, Hazzard MP, Mahood NV, Castellani JW. Thirst sensations and AVP responses at rest and during exercise-cold exposure. Med Sci Sports Exerc. 2004.
- King N, Roberts DE, Edwards JS, Morizen RD, Askew EW. Cold-weather field feeding: an overview. Mil Med. 1994.
- Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988.
- Beard JL, Borel MJ, Derr J. Impaired thermoregulation and thyroid function in iron-deficiency anemia. Am J Clin Nutr. 1990.
- MedlinePlus Medical Encyclopedia. Dietary fats explained. U.S. National Library of Medicine.
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
