Having persistently high blood sugar levels through the day can result from a number of possible reasons.

How you respond to the high sugar levels will depend on the cause.

If you need to increase your insulin doses, proceed with caution so as not to significantly increase the risk of hypoglycemia occurring.

  1. Missing insulin injections
  2. Underestimating insulin taken with meals
  3. Periods of illness or infection
  4. Less activity than normal
  5. Changes in climate/seasons
  6. Puberty
  7. Periods
  8. Honeymoon period ending
  9. Gaining significant weight
  10. Taking certain medication
  11. Too little background insulin

1. Missing insulin injections

We should all be aware that missing insulin injections will result in high blood glucose levels.


At first you may need to set reminders to get into the habit of taking your injections. Sometimes being busy or distracted around meal of bed times can lead to insulin injections being forgotten. If this is the case, make a habit of not rushing meals or getting to bed and give yourself room to focus on your diabetes and your injections.

Important note
If you have any doubts in assessing the cause of your high sugar levels or how best to adjust your insulin, contact your health team who will be able to advise you. If increasing insulin doses, make sure your health team are happy for you to do so and take care to avoid increasing the risk of hypos occurring.

2. Consistently underestimating how much insulin to take with meals

If you are regularly getting too high sugar levels, one of the first questions to ask is whether you’re taking enough insulin before meals.


If you’re finding it difficult to judge your insulin doses, ask your health team about going onto a carbohydrate counting course

3. Period of illness/infection

Illness and infection can cause the body to become less sensitive to insulin which can cause stubbornly high blood glucose levels for a few days.

If you are injecting insulin to correct high sugar levels but to little effect, a period of illness is a possible cause.


If you’ve been on a DAFNE course, or similar carbohydrate counting course, following the advised sick day rules. If you’ve not been on one of these courses, it’s best to ask your health team how best to respond to periods of illness.

4. Being less active than you usually are

Physical activity improves insulin sensitivity Therefore, if you have been less active than you usually are, this can result in higher than normal sugar levels.


Consider taking more activity on less active days. If this is not possible, you may consider raising one or more of your insulin doses.

5. Changes in climate/seasons

Changes in climate and temperature can lead to changes in insulin demands. Spells of colder weather is more commonly associated with rises in blood glucose levels. [123]


Consider increasing your background insulin to counteract the rise in blood glucose levels.

6. Going through puberty

Research shows that during puberty, the body becomes more resistant to the effects of insulin. In addition, insulin demand increases as we grow. Therefore, you may find you need to gradually increase your intake as you go through your teenage years. [124] [125]


You may need to increase doses of background insulin as well as doses of short or rapid acting insulin. Your health team can help you with getting the right balance of insulin doses.

7. Periods

The change in levels of the hormones oestrogen and progesterone can lead to temporary insulin resistance either before or during your period

The effect on blood sugar levels can vary from person to person and from period to period. Usually the reduced sensitivity to insulin lasts no more than a few days.


Depending on how consistent the affect on your sugar levels is, you may want to increase one or more of your insulin doses at the point of your period you are getting high sugar levels.

If the affect on your sugar levels is not consistent, it may be risky to increase insulin doses. Speak with your health team if you need help with managing your diabetes during your period.

8. Honeymoon period wearing off

The honeymoon period describes a period of time following your diagnosis when your pancreas is still able to produce enough insulin to influence blood glucose levels. As the autoimmune effect of type 1 diabetes continues, however, your pancreas will be able to produce less and less insulin.

The honeymoon period usually takes between several months and a few years to wear off and as it does, your sugar levels through the day will begin to rise.


If your honeymoon period is coming to an end, you will likely need to increase insulin doses as a result. Speak to your health team if you need any advice in getting the right balance of insulin doses.

9. Weight gain

A significant increase in body weight may lead to higher than usual blood glucose levels.

Putting on a few pounds shouldn’t affect your blood glucose levels but if you’ve put on close to a stone (over 6 kg) or more, this could lead to an increase in blood sugar levels and an increased demand for insulin.


Losing weight can help to improve insulin sensitivity. You may also need to increase one or more of your insulin doses in the mean time.

10. Taking certain medication

Some medications are known to increase blood glucose levels, particularly if taken in higher doses or over long periods of time.

Such medications may include:

If in doubt, check the patient information leaflet to see whether it lists an increased risk of hyperglycemia.


The action you may need to take will depend on a number of factors, including the medication you’re taking. It’s best to consult your health for help with this matter.

Also notify your GP or health team if you’re having difficulty controlling your blood glucose levels since you’ve been put on a new medication or a new dose of it.

11. Too little long acting/intermediate insulin

The above reasons present a series of possible causes of high sugar levels. If the cause of high sugar levels is not related to a temporary factor (eg illness or before or during your period) then you may need to increase your basal insulin (intermediate or long acting insulin).

As always, if ever in doubt about how to best manage your insulin, speak to your diabetes health team.

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