3 min readNew DelhiApr 30, 2025 08:26 PM IST
First published on: Apr 30, 2025 at 07:26 AM IST
One of my patients has taken my advice on keeping to a morning walking routine of 30-40 minutes and gets out of the house at 8 am. The other day he told me that despite sweating it out in the hot and sultry weather, his blood sugar levels were fluctuating a lot, “Sometimes they drop too low, and at other times they go unusually high. Is this normal?,” he asked.
The answer is yes. In hot and humid weather, your body’s response to exercise can change, especially when you have diabetes. The heat affects how your body uses the sugar-regulating hormone insulin and how quickly it absorbs medication. That can cause unexpected blood sugar highs or lows.
But I thought exercise usually helps lower blood sugar?
It does. But in hot weather, your body dehydrates faster, which concentrates your blood glucose and may cause high readings. At the same time, heat can increase insulin absorption, making it act quicker and possibly leading to sudden lows or hypoglycaemia. So yes, both highs and lows are possible.
Does that mean I should stop exercising until the weather improves?
Not at all but exercise with precautions—stay well-hydrated, avoid peak heat hours, wear light breathable clothes, and always carry a quick-acting carb. Also, it’s better to change the timing of your walk, from 8 am to evening hours. Or try waking up earlier and walk between 5.30 and 6 am, when it is cooler and more pleasant. There’s less pollution too, so your breathing and heart rate will respond better.
If you try waking up just two hours earlier, your body will adjust over time.
Sometimes my sugar goes up right after I start walking. Why does that happen?
When you begin exercising, your heart rate increases and the liver releases stored glucose to give you energy. That’s why your blood sugar can go high initially. But after a while, your muscles will start using up that glucose, and your sugar will gradually come down.
Does going to an air-conditioned gym help?
Air-conditioned indoor spaces can reduce the risk of overheating and dehydration. But because the environs are cooler, your body may not burn quite as much energy. Still, it’s a good and safe option during summer.
How can I better track my blood sugar levels amid fluctuations?
You can consider using a Continuous Glucose Monitor (CGM). It tracks your glucose throughout the day, including before, during and after exercise. It’s especially useful in managing sudden highs and lows and gives you real-time feedback.
Do I need to change my medication because of this?
Only if the fluctuations continue. First monitor your readings for a week—preferably using a glucometer or CGM. Based on the trends, dosage can be adjusted.
Be vigilant about hypoglycemia symptoms like dizziness, sweating or palpitations. Also, if your sugars stay high despite exercise, we’ll need to rule out dehydration or other metabolic issues. Don’t skip your post-exercise snack if you’ve been advised to have one.
(Dr Mohan is Chairman, Dr Mohan’s Diabetes Specialities Centre, Chennai)
When you begin exercising, your heart rate increases and the liver releases stored glucose to give you energy. That’s why your blood sugar can go high initially. 
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