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Hot Weather and Blood Sugar: Heat, Cold and Insulin Storage

Key Takeaways

  • People with diabetes can get dehydrated faster in the heat, and heat can change how the body uses insulin.[1]
  • The FDA says insulin can stay out of the fridge at 59°F to 86°F (about 15°C to 30°C) for up to 28 days. Never use insulin that has frozen.[2]
  • Heat and cold can both damage meters, pumps, CGMs and test strips.[1][3]
  • Large studies have found A1C runs a little higher in winter, though the pattern varies by climate.[4][5]

Hot weather and blood sugar are connected in several ways. The CDC says people with diabetes get dehydrated more quickly, that high temperatures can change how the body uses insulin and that heat can damage diabetes equipment. It advises testing more often in hot weather.[1] Cold weather brings its own changes, from stress hormones to frozen insulin.

Storage rules for insulin and meters are in a table further down, with the source for each figure. This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

How are hot weather and blood sugar linked?

In three ways: dehydration, cooling and insulin. The CDC says people with diabetes lose water from their bodies more quickly, and that diabetes can affect the sweat glands so the body cannot cool as well.[1] A small study of active men found that those with type 2 diabetes lost less heat during exercise in hot conditions than those without, because they lost less heat through sweating.[6]

The CDC suggests you may need to test your blood sugar more often in the heat and adjust your insulin dose and what you eat and drink, with advice from your team.[1] It also notes that sunburn can raise blood sugar, so wear sunscreen and a hat outside.[1] Drinking enough water helps. Our guide to hydration and diabetes explains why. The NHS says to call 999 if someone in the heat is still unwell after 30 minutes of cooling, feels hot and is not sweating, is confused, has a fit or is not responsive. In the US, call 911.[7]

Heat and insulin absorption: does heat change how insulin works?

It can. The CDC says high temperatures can change how your body uses insulin.[1] Older research found that higher temperatures speed up the absorption of soluble, rapid-acting insulin. A 1983 sauna study in 8 people with type 1 diabetes then found no such effect for an intermediate-acting insulin.[8] Those were older insulins, so ask your team how heat may affect the one you use.

If you use insulin or a sulfonylurea such as gliclazide or glimepiride, hot weather and faster insulin absorption can make low blood sugar more likely.[1][8][9] Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.[9][10] In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.[9] In the US, the ADA says to call 911 right away if someone is unconscious and glucagon is not available or no one knows how to use it.[10] Learn the signs of low blood sugar before hot days and holidays.

Storing insulin in heat: how do I protect insulin and meters?

The FDA recommends storing insulin in a fridge at about 36°F to 46°F (about 2°C to 8°C). Vials and cartridges, opened or unopened, can be kept out of the fridge at 59°F to 86°F (about 15°C to 30°C) for up to 28 days and still work. Keep insulin away from direct heat and sunlight.[2] Some products have different limits, so check the leaflet that comes with yours.

  1. Store unopened insulin in the fridge at 36°F to 46°F (about 2°C to 8°C). Vials and cartridges in use can stay at 59°F to 86°F (about 15°C to 30°C) for up to 28 days, or as your product leaflet states.[2]
  2. Never store insulin or diabetes tablets in direct sunlight or in a hot car.[1]
  3. Keep your meter, pump, CGM and test strips out of hot cars, direct sun and freezing cold. Use a cool bag, but do not put insulin directly on ice or a gel pack.[1][3]
  4. Check that your home fridge holds the right range. In one study, insulin stored in home fridges was outside the recommended range 11.3% of the time.[11]
Pro Tip

A cheap fridge thermometer placed next to your insulin shows whether it stays between 2°C and 8°C (36°F and 46°F). In the same study, 57 of the 230 fridge sensors recorded a temperature below 0°C (32°F) at some point.[11]

When we checked the FDA and CDC pages for this guide, both gave the same rule on frozen insulin: do not use it, even after it thaws.[1][2][3]

Item. Safe range. Practical point.
Insulin in the fridge.[2] 36°F to 46°F (about 2°C to 8°C).[2] Keep a thermometer on the shelf next to the insulin.[11]
Vials and cartridges out of the fridge.[2] 59°F to 86°F (about 15°C to 30°C) for up to 28 days.[2] Check your insulin leaflet, as some products have different day limits.[2]
Insulin that has frozen.[2][3] Do not use, even after thawing.[2][3] Use a spare vial or pen instead.[2]
Meters, pumps and test strips.[1][3] Keep out of hot cars, direct sun and freezing cold.[1][3] Meters took 15 to 30 minutes to settle after a move from heat or cold.[12]

Cold weather and blood sugar: does the cold raise it?

It can. The CDC explains that cold temperatures stress the body, and the stress hormones released prompt the liver to release more sugar, so blood sugar levels go up.[3] For more on this effect, see our guide to stress and glucose levels.

Cold also affects your kit. The CDC says frozen insulin no longer works, even when thawed, and that cold can damage insulin pumps and CGMs.[3] The FDA also says not to use insulin that has been frozen.[2] If your hands are cold, the CDC suggests warming them near a heater or around a cup of warm water before a finger-prick test.[3]

Meters need time to adjust too. In a lab test, meters took 15 to 30 minutes to give stable readings after being moved from heat or cold to room temperature, while the strips were little affected.[12]

What changes in winter?

A study of more than 285,000 US veterans with diabetes found A1C was higher in winter than in summer by 0.22 percentage points (about 2.4 mmol/mol), with bigger gaps in colder regions.[4] A clinic study of 638 people with type 2 diabetes in Greece also found fasting glucose and HbA1c were higher in colder months.[13]

The pattern is not the same everywhere. In a study of 8,138 people in India, HbA1c peaked during the monsoon from June to September.[5] Local climate and daily habits seem to matter. Staying active indoors in bad weather can help. See our guide to exercise and blood sugar for ideas.

Questions to ask your diabetes team

  • What room-temperature day limit and range apply to the insulin pens or vials I use?[2]
  • I use insulin or a sulfonylurea such as gliclazide or glimepiride. How should I check my glucose and adjust my plan in a heatwave or on a summer holiday?[1][8][9]
  • How should I carry my insulin, pump or CGM when travelling in very hot or freezing weather?[1][2][3]
  • What should I do if my insulin gets too hot or freezes, or my meter gives odd readings in extreme weather?[2][3][12]

Frequently asked questions

Can hot weather make blood sugar go up or down?

It can. The CDC says heat can change how the body uses insulin, that dehydration and sunburn can raise blood sugar, and that you should know the signs of a low. It advises checking your blood sugar more often in hot weather.[1][8]

How long can insulin stay out of the fridge?

The FDA says vials and cartridges can be kept at 59°F to 86°F (about 15°C to 30°C) for up to 28 days. Check your product leaflet, because some insulins differ.[2]

Can I use insulin that has frozen?

No. The CDC and the FDA both say not to use insulin that has been frozen, even after it thaws.[2][3]

Is blood sugar higher in winter?

A large US study and a smaller Greek clinic study found slightly higher A1C or fasting glucose in colder months. A study in India found a peak during the monsoon instead, so the pattern depends on climate and lifestyle.[4][13][5]

Where to go next

For more on hot weather and blood sugar, see:

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.

Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Talk to your doctor before changing your diet, your activity or your medicines, and before starting any supplement.

Sources & References

  1. Centers for Disease Control and Prevention. Managing Diabetes in the Heat. cdc.gov Funding: not applicable, this is official guidance, not a funded study.
  2. U.S. Food and Drug Administration. Information Regarding Insulin Storage and Switching Between Products in an Emergency. fda.gov Funding: not applicable, this is official guidance, not a funded study.
  3. Centers for Disease Control and Prevention. Managing Diabetes in Cold Weather. cdc.gov Funding: not applicable, this is official guidance, not a funded study.
  4. Tseng, C. L., et al. (2005). Seasonal patterns in monthly hemoglobin A1c values. American Journal of Epidemiology. pubmed.ncbi.nlm.nih.gov/15746473 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  5. Ahuja, S., et al. (2024). Seasonal variation of HbA1c levels in diabetic and non-diabetic patients. Practical Laboratory Medicine. pubmed.ncbi.nlm.nih.gov/38711868 Funding: none listed on the PubMed record. COI: The authors have no conflicts of interest to declare.
  6. Notley, S. R., et al. (2019). Exercise Heat Stress in Patients With and Without Type 2 Diabetes. JAMA. pubmed.ncbi.nlm.nih.gov/31593261 Funding: CIHR (grants listed on PubMed). COI: Conflict of Interest Disclosures: Dr Kenny reported receiving grants from the Canadian Institutes of Health Research. No other disclosures were reported.
  7. NHS. Heat exhaustion and heatstroke. nhs.uk Funding: not applicable, this is official guidance, not a funded study.
  8. Koivisto, V. A. (1983). Influence of heat on insulin absorption: different effects on amorphous and soluble insulins. Acta Diabetologica Latina. pubmed.ncbi.nlm.nih.gov/6349204 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  9. NHS (reviewed 3 August 2023). Low blood sugar (hypoglycaemia). nhs.uk Funding: not applicable, this is official guidance, not a funded study.
  10. American Diabetes Association. Hypoglycemia (low blood glucose): symptoms and treatment. Accessed 1 November 2026. diabetes.org Funding: not applicable, this is official guidance, not a funded study.
  11. Braune, K., et al. (2019). Storage Conditions of Insulin in Domestic Refrigerators and When Carried by Patients: Often Outside Recommended Temperature Range. Diabetes Technology & Therapeutics. pubmed.ncbi.nlm.nih.gov/31009254 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  12. Deakin, S., et al. (2015). Cook and Chill: Effect of Temperature on the Performance of Nonequilibrated Blood Glucose Meters. Journal of Diabetes Science and Technology. pubmed.ncbi.nlm.nih.gov/26292960 Funding: none listed on the PubMed record. COI: Declaration of Conflicting Interests: The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: 1. AccuNostics employees as part of their remuneration package receive share options in the company 2. DK has received consultancy fees from AccuNostics, Abbott Diabetes Care, and Roche Diagnostics. 3. RL is a former employee of Roche and owns shares in Johnson & Johnson and Roche.
  13. Gikas, A., et al. (2009). Seasonal variation in fasting glucose and HbA1c in patients with type 2 diabetes. Primary Care Diabetes. pubmed.ncbi.nlm.nih.gov/19535310 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
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