News · Heart & Metabolic
Mild cold lowered blood sugar. Colder did nothing.
A Diabetologia trial put people in a water-cooled suit until they shivered. In type 2 diabetes, the gentler cold cut 24-hour glucose. The harder cold did not.
Based on a peer-reviewed randomized crossover trial in Diabetologia
- Researchers cooled sedentary, non-smoking adults with prediabetes or type 2 diabetes in a water-perfused suit, publishing in Diabetologia.
- Each person did two sessions in randomized order: mild cold at 15C and moderate cold at 4C, designed to raise resting metabolic rate about 1.5-fold and 2.5-fold.
- Shivering was confirmed objectively with indirect calorimetry and muscle electrical activity, not assumed.
- Continuous glucose monitors tracked 24 hours before and after each session, with diet and activity controlled.
- In type 2 diabetes, mild cold lowered mean 24-hour glucose by 0.6 mmol/l and fasting glucose by 0.6 mmol/l, and raised time in normal range by 8.8 percentage points.
- Moderate cold did not significantly affect any glucose outcome in type 2 diabetes.
- In prediabetes, neither intensity changed mean 24-hour glucose at all.
- Participants were masked to the cold intensity but investigators were not, and there was no thermoneutral control condition.
- Acute effects only. This tested single sessions, not a repeated program, and the authors call for larger validation.
Cold plunges are sold on a long list of promises, most of them untested. A trial in Diabetologia tested one of the more plausible ones under laboratory control, and got a result that argues against the assumption underneath the whole trend: that colder is better.
The researchers aimed to determine whether cold exposure at two different intensities improves 24 h glucose homeostasis in individuals with prediabetes and type 2 diabetes.
Making cold measurable
The problem with studying cold is that people experience it differently. This design removed that.
Participants, who were non-smoking and sedentary, underwent two whole-body cold exposure sessions using a water-perfused suit - a garment with water circulating through it at a set temperature, so the dose is controlled rather than left to a thermostat and a shivering volunteer.
Sessions were designed to elicit approximately 1.5-fold (mild, 15C) and 2.5-fold (moderate, 4C) increases in resting metabolic rate. Session order was randomized, and participants were masked to the cold exposure intensity received, though investigators were not.
Shivering was not taken on trust. It was confirmed via indirect calorimetry and electromyography, meaning both the energy burn and the muscle electrical activity were measured.
Then continuous glucose monitoring assessed interstitial glucose concentrations over 24 h periods before and after each intervention, with controlled diet and activity. Not a single fasting reading the next morning, but a whole day, with food and movement held steady.
The cold worked as cold
The physiology behaved. In both study groups and periods, resting metabolic rate increased significantly versus baseline.
In the type 2 diabetes group the increase reached about 1.57 times baseline in mild cold and 2.09 times in moderate. People were genuinely cold and genuinely burning more fuel, and the harder condition was harder.
The glucose did not follow
Here the expected pattern breaks.
In prediabetes, neither mild nor moderate cold exposure altered mean 24 h glucose levels. Nothing, at either dose.
In type 2 diabetes, the mild condition did something. After mild cold exposure the type 2 diabetes group exhibited a significant reduction in mean 24 h glucose levels of 0.6 mmol/l, along with the same fall in fasting glucose, an increase in time in normal range of nearly 9 percentage points, and roughly 11 fewer percentage points of the day spent with high glucose.
And the harder cold, the one that nearly doubled energy expenditure? Moderate cold did not significantly affect any glucose outcomes in type 2 diabetes.
More shivering. More fuel burned. No glucose benefit.
Why that shape matters
A treatment that works at a low dose and stops working at a higher one is not behaving like a simple fuel-burning effect. If glucose uptake during shivering explained the result, more shivering should mean more uptake.
The authors reach the same conclusion: the observed effects appear to depend on baseline metabolic status rather than acute substrate use during cold exposure.
Their predictor analysis points the same way. Baseline fasting glucose, age and liver enzyme levels predicted who responded, suggesting greater benefits in individuals who have higher baseline glucose levels, are younger and/or have more optimal liver health.
So the people who improved were those with the most disrupted glucose control to begin with, which is why prediabetes showed nothing.
The limits, which are real
There is no thermoneutral control condition. Everyone got cold; the comparison is mild against moderate, not cold against no cold. That leaves open how much of the mild-cold improvement reflects cold at all rather than a day in a laboratory with controlled food and no exercise.
Investigators were not masked, and the sample is small, sedentary and specifically selected. These are acute single sessions, so nothing here shows what a repeated program would do, or whether the effect persists past a day.
And the practical translation is not obvious. A water-perfused suit at a controlled 15C is a laboratory instrument. An ice bath is a much harsher stimulus, closer to the condition that did not work, and it carries cardiovascular load that matters in a population where heart disease is common.
What it is good for
The authors put it at the right level: these findings support the potential of cold exposure as an adjunct non-pharmacological therapy for type 2 diabetes, although further mechanistic studies and validation in larger cohorts are warranted.
Potential, adjunct, and warranted further study. What the trial adds beyond that is a specific warning to the wellness version of this idea: the dose that helped was the mild one, and pushing harder bought nothing at all.
People also ask
Why would being cold lower blood sugar?
Shivering is muscle contraction, and contracting muscle takes up glucose from the blood through a route that does not depend on insulin. That is the same back door exercise uses, which is why both can help when insulin signaling is impaired. Cold also activates brown fat, which burns fuel to make heat, though this study found the effect depended on baseline metabolic status rather than on what was being burned during the cold itself.
Why did the harder cold not work better?
Nobody knows, and it is the study's most striking result. More shivering meant more energy expenditure, which the measurements confirmed, but that did not translate into lower glucose over the next 24 hours. One possibility is that the more demanding session provoked a stress response that pushed glucose the other way, offsetting the uptake. The paper does not resolve it, and a dose-response that goes up and then flattens is a reason for caution rather than enthusiasm.
Should someone with diabetes try cold showers or ice baths?
This is general information, not medical advice, and the answer is not yet. This trial used a temperature-controlled water-perfused suit under supervision, which is not the same as a cold shower or an ice bath. Cold exposure raises blood pressure and cardiac workload, which matters given how often type 2 diabetes travels with heart disease. Anyone considering it should discuss it with their own clinician first, and nobody should alter medication based on this.
Why did it not work in prediabetes?
The authors suggest the response depends on baseline metabolic status. People with prediabetes have more glucose control left intact, so there is less room to improve and less dysfunction to correct. Consistent with that, the predictors of a good response were higher baseline glucose, younger age and better liver health. The people who benefited were the ones with the most to gain.
How strong is this evidence?
It is a randomized crossover trial with objectively confirmed shivering and continuous glucose monitoring, which is a genuinely rigorous setup for a mechanism study. It is also small, acute, and lacks a thermoneutral control condition, so the comparison is between two cold doses rather than against no cold at all. The authors explicitly call for mechanistic work and validation in larger cohorts.
References
- Hashim D, Jorgensen JA, van de Weijer T, Blondin DP, Schrauwen P, Hoeks J. Acute mild cold exposure with shivering reduces 24 h glucose levels in individuals with type 2 diabetes but not prediabetes. Diabetologia (2026).
- National Institute of Diabetes and Digestive and Kidney Diseases. Managing Diabetes.
- Centers for Disease Control and Prevention. Diabetes and Your Heart.