10 surprising causes of blood sugar fluctuations

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Altered sleep patterns, dehydration, stress and a number of other everyday occurrences can cause fluctuations in your blood sugar.

What is diabetes?

Diabetes mellitus is a condition where the body does not produce enough insulin, or where it does not respond to insulin in a normal way.

Insulin is a hormone produced in the pancreas which acts to move sugar into cells to be used as energy, and when our blood sugar becomes too low or too high, it can cause serious problems.

Diabetes is a growing concern worldwide, and contributes to the development of other serious illnesses like heart disease, stroke, and other vascular conditions.

People with type 1 diabetes typically have the condition from childhood, or as a result of a problem with the pancreas developing later in life.

It isn't usually easy to predict who will have type 1 diabetes. The main treatment pathway for type 1 diabetes is insulin injections tailored to regular blood sugar monitoring.

People with type 2 diabetes may have more treatment options, ranging from simple diet management through to tablets, injectable non-insulin diabetes medications, and insulin injections. Some of the risk factors for developing type 2 diabetes including being overweight or obese, having a sedentary lifestyle, and carrying excess fat around the middle.

Sometimes diabetes develops in pregnancy, and is called gestational diabetes. This is associated with some risks to mother and baby, so needs to be closely managed.

Gestational diabetes usually resolves after birth, but people who experienced gestational diabetes seem to be at a higher risk of going on to develop type 2 diabetes later in life.

Why does blood sugar fluctuate, and how do I know when it happens?

Small fluctuations in blood sugar readings are normal, and blood sugar varies throughout the day and depending on activity, diet and a number of other factors. In non-diabetic people, these fluctuations are usually minimal, as the amount of sugar in the blood is carefully regulated by the body's natural processes and insulin secretion.

We don't know exactly how high or low our blood sugar is unless it is tested. This is usually done with a fingerprick test, where a drop of blood placed on a machine is analysed. Specialists may refer to these as capillary blood glucose — CBG.

This can be done at home, and people who take insulin may have to check their blood sugar readings several times a day. Large fluctuations in blood sugar may cause symptoms like fatigue, confusion, dry mouth, headaches and blurred vision.

Untreated critically out-of-range blood sugar levels can have extremely serious long- and short-term effects.

Diet and fluid intake

It shouldn't come as much surprise to learn that the things you eat affect your blood sugars. It's not just simple sugars, sweets and puddings that can send blood sugar levels soaring. Some fruits are notorious for sending blood sugars out of range, with unexpectedly high sugar levels.

Dried fruit in particular is a dense source of sugar. Fruit is still good for you, full of fibre and vitamins, so most people shouldn't totally avoid it; just be mindful of the amount of sugar in some fruits.

Maintaining a healthy diet and weight is important for lots of reasons, and one of the most significant is reducing the risk of type 2 diabetes.

In general, the more fat we carry, the less sensitive our body can become to the insulin we naturally release. Without insulin effectively controlling our blood sugar, we can develop type 2 diabetes and increase our risk of many serious health conditions.

Dehydration can also play a huge part in blood sugar control. Being dehydrated causes higher blood sugar levels, causing extreme thirst and, long-term, causing serious problems with the small blood vessels of the body.

People who take insulin may follow a regime where they take a measured dose of short-acting insulin to match the carbohydrate content of a meal.

Artificial sweeteners

Sugar-filled soft drinks are an often-overlooked route for lots of sugar to enter our diet, but it actually, sugar-free diet soft drinks seem to have a negative effect on our insulin sensitivity and blood sugar control too.

Artificial sweeteners can be found in all sorts of food and drinks, but are most commonly found in soft drinks and yoghurts. Any sweet-tasting food that's sold as 'sugar-free' or 'diet' is likely to contain artificial sweeteners.

Although artificial sweeteners don't have the same kind of immediate blood sugar boosting effect that sugar has, regular consumption of artificial sweeteners affects the way we metabolise glucose.


Some people find that their blood glucose levels fluctuate in line with their menstrual period, and diabetics may have to be mindful of this and adjust their treatment accordingly.

Pregnancy is also a time of fluctuating blood sugars, and those who develop gestational diabetes need to be very closely monitored and managed to prevent any complications.

Those having hormone treatment may also find that their blood sugars are affected, and if this is likely to be the case, the doctor prescribing the treatment should be able to give some advice or direction. Some hormone treatments might actually help to regulate blood sugars.


Many medications have side effects, and some can actually cause deranged blood sugar levels. Steroids like prednisolone, often taken for inflammatory or autoimmune conditions, or exacerbations of certain lung diseases, are particularly well known for causing blood sugars to rise.

People who take high doses of these kinds of steroids may need to have their blood sugar levels checked.

Some medications given for diabetes —  metformin, gliclazide and more —  have an effect on blood sugar. Some work by improving the way our body makes and uses insulin, others change the way our liver releases sugar into the blood.

Some medications are designed to have a long-term effect on diabetes management, whereas others have a more immediate effect on blood sugars. Sometimes it takes a little time and experimentation for doctors to get the doses and timings of diabetic medications exactly right for the individual patient.

Poor sleep

Poor sleep and unstable sleep patterns can have an effect on blood sugar levels. Our bodies naturally try and regulate blood sugars and insulin release according to our circadian rhythm — the natural pattern of wakefulness and sleep.

Diabetics who work varying shift patterns which include night shifts may particularly find it hard to stick to a healthy routine for blood sugar control. Anything that disturbs sleep — a new baby in the family, illness or caring responsibilities — can affect circadian rhythm and impact blood sugar control.

The correlation goes both ways — just as fluctuating sleep patterns can have an effect on our blood sugar, diabetics may find that having unstable blood sugars makes for a poor night's sleep.

Healthy bodies naturally regulate insulin and blood glucose overnight to maintain stable blood sugars, but people who are prone to unstable blood sugars may find that they wake up with out-of-range blood sugars.

Timing meals, eating slow-release carbohydrates like wholegrain foods, and keeping a close eye on blood sugars around bedtime and first thing in the morning can help people reach stable blood sugars.

Diabetics and non-diabetics alike can find that bad night's sleep can leave us feeling exhausted and run-down. Even non-diabetics show more fluctuations in blood sugar when they're sleep deprived compared to when they've had a reasonable night's sleep.

This tiredness can also make us feel hungry, turning to sweet snacks to try and compensate for the low energy levels of fatigue.


Caffeine has a significant effect on blood glucose management in type 2 diabetics, and may also contribute to the development of type 2 diabetes.

Caffeine has long been a controversial factor in discussion of blood glucose control, and there have been some suggestions that some caffeinated drinks have some protective qualities.

However, the most recent high quality studies have found that a negative impact from caffeine on blood sugar management.


Stress — whether family and personal worries, pressures at work, injury, illness, or any of the myriad other stressors in our modern lives — has a complicated relationship with blood sugar control. Not just acute stress, but longer-term mental health conditions, anxiety and depression all have an impact on the way our bodies regulate insulin and blood sugar.

The impact of this is most likely to be serious in diabetics, but can affect anybody, diabetic or not. There is an idea that longer-term, heightened stress levels maintain the body in a low-key 'fight or flight' type state, meaning that the nervous system is poised ready to give the body more glucose.

In fact, the correlation is likely to be complex, and involve the impact of stress and mental illness on other aspects of life, including sleep, diet, activity, and use of alcohol and caffeine.


When we exercise, we need extra energy, in the form of glucose, to be available to use in our cells. We also need insulin to enable those cells to retrieve and use the sugar from our blood circulation. One immediate effect of exercise is to lower the blood sugar, as we use up energy with activity. The length and intensity of a workout affects its impact on blood sugars.

Diabetics, particularly those who use insulin, may be advised to check their blood sugar levels before and after a workout or any sustained intense activity.

There is some evidence that exercising in the afternoon is of the most benefit to blood sugar levels, in keeping with the body's circadian rhythm and natural energy level fluctuations.

Longer-term, having an active lifestyle with plenty of healthy exercise may have a positive impact on blood sugar control, diabetes risk, and management of existing diabetes.

Being active is one of the best things we can do to improve our overall health and reduce our risk of type 2 diabetes. Exercise is excellent for weight control, and we know that being overweight or obese is one of the highest predictors for type 2 diabetes.

Regular, high intensity exercise has both short- and long-term benefits on blood sugars for non-diabetics, and significantly decreases the risk of developing type 2 diabetes.


Acute illness is closely associated with fluctuations in blood glucose levels. The physical stress of illness, the use of some medications, and the impact of illness on other aspects of life like sleep quality, hydration and nutrition all contribute to unstable blood sugars.

It isn't always possible to avoid an acute illness, but diabetics should be mindful of the potential effect of illness on their blood sugar control.


Alcohol is metabolised in a similar way to other simple sugars, and usually causes an initial spike in blood sugar immediately after consumption. Unlike other sugars, alcohol affects the liver's ability to deliver glucose into the blood stream, meaning that after an initial spike, blood sugars can dip significantly.

People with insulin-controlled diabetes mellitus are more likely to have hypoglycaemia — abnormally or dangerously low blood sugar levels — the morning after an evening of moderate to heavy alcohol intake.

Alcohol is also a source of empty calories, which can contribute to weight gain for some people, increasing insulin resistance and the risk of type 2 diabetes.

Maintaining healthy blood sugar levels

Type 2 diabetes risk and management can respond well to lifestyle changes — diet, good amounts of exercise, and maintaining a healthy weight all go a long way towards preventing or reducing the impact of the condition.

Managing our alcohol intake and being aware of hidden sugars in our diet — and the possible impact of artificial sweeteners — can also help.

Being aware of some of the more unexpected causes of blood sugar fluctuations is important to help us make healthy choices and to care for ourselves, and our loved ones, properly.

It isn't always possible to avoid stress, hormonal fluctuations, and acute illness, but just knowing the effect they might have can help us spot warning signs.

Looking after our existing conditions can help keep us healthy, and it's easier than ever with telehealth facilities, home visits and medication delivery services.

For those who struggle with their diabetes management, specialist carers can help with blood glucose monitoring, with remembering to take medications, insulin administration, and any aspect of healthy lifestyle management.

READ MORE: Insulin 101: How it works, types, delivery & more

This article was first published in Homage.

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