Basal insulins

What is basal insulin for?

The body needs glucose and insulin to operate and for your brain to function – to enable you to breathe in and out, for your heart to pump blood round your body, your digestive system to digest, your nerves to function etc etc. So you need it 24 hours a day, 365 days a year forever – whether awake, resting or active, asleep, anaesthetised, comatose.

Type 1 or Type 2 – if your body produces no insulin at all or only reduced levels – then we need to add it via injections in order to merely stay in the land of the living.

Basal insulin is intended to cover only that background need.

Then when you eat something again the body requires insulin to deal with what you ate, but at a much faster rate than any basal insulin delivered once or twice a day, therefore faster-acting insulin is added at mealtimes to cover that need. If your basal insulin dose is incorrect then you may find you are running constantly high (or low) blood sugar levels between meals or before any meal and the temptation is to just give yourself more (or less) mealtime fast-acting to adjust this.

That’s fairly OK and accepted if it only happens occasionally – but when you have to do it all the while – and you may not even actually realise that is what you are doing! – then it all needs sorting out. And you need to learn both what’s happening with your body and with your insulin, in order to understand both what is happening to you – and why it is happening. I’ll try and explain.

Different insulins (basal and bolus) have different ‘active life’ profiles, which all peak at some time or another to some extent or another. Only generally can the profile be predicted – as the details will differ from patient to patient.

So – you really do have to find out for yourself!

It is an out and out total misunderstanding – held by many doctors and patients – that Lantus always lasts for 24 hours and releases itself steadily throughout that period.

Medics will tell you to inject it once a day at the same time each day, usually at bedtime.

In fact – it builds up to a steady-ish rate over an hour or two, then has a ‘mini-peak’ for a while, then steadies for a longer while, then gradually tails off. See here for diagram. You might need more at night and less in the day – or vice versa.

Need more at night – then taking it at bedtime is probably a good plan, so it peaks whilst you need more. You should not regularly need to increase your blood sugar to a level in excess of c.7.0 before bed in order to avoid hypos during the night or early morning – this shows you that something is wrong.

Need less at night – try taking it when you get up – that way it should be tailing off when you go to bed and sleep, whilst you need less.

The total active period for you can be as short as 18 hours or as long as 36 hours. No-one can predict this for you.

Try splitting your dose – this sometimes works on a 12 hour split but often it doesn’t. It may involve different dosages morning and evening or night and morning – everyone is different and it can be easy or quite difficult sometimes to a) get it right and b) to even keep track of what you’ve tried and how it affected you.

Lantus is notorious for taking at least 3 days to establish a pattern. For some that will be it – sorted. For others it works like a dream after that for a while – days or weeks, even months before it fails. So you need to start over – or consider changing your Lantus for Levemir.

NB 2. The Lantus Optiset pen can be a hindrance when you are trying to make minor adjustments (fine tuning) especially if you are using comparatively low overall dosages or need an ‘odd’ number of units, because the minimum delivery is in 2 unit increments. There are other pens available and if you are happy with the insulin otherwise, just request a different type of pen from your doctor.


Levemir lasts for 12 – 15 hours. It is rare to find anyone for whom it lasts for the full 24. It does peak and subsequently tail off – see here.

but because it does seem to be rather more predictable – and its effects are always of shorter duration than Lantus – if you do need differential rates during each 24 hour period, it is usually far easier to achieve this using Levemir.

Whilst these days many are prescribed Levemir 2 x daily instead of Lantus x 1 from the outset – there seems not much evidence as to why we usually ‘automatically’ get one or the other. If you want to ‘have a go’ with the other one and your doctor doesn’t have a reason – then ask to change, they shouldn’t bar you from doing so.

Some medics just have the false idea that one more little injection a day is going to cause us stress and anguish – in point of fact it often cures that very thing – when it leads to our having better control !

If the medic has a reason – then he shouldn’t have any trouble explaining it to you and either obtaining your agreement – or not.

How to discover (or adjust) your basal insulin dose

You can do this in any order, but you do need to be methodical and keep records. It isn’t usually achieved within days. Take comfort that once you do get it ‘about right’ the fine-tuning dose adjustment process becomes simpler.

If you start with overnight – it makes the other ones look easy! I think it is less daunting to start with the morning and gradually work through the day and evening – by the time you get to ‘overnight’ you’ll be familiar with the process.


Get up, test your BS, take any medications you require including basal insulin if that’s when you normally take it. Do not take any fast-acting insulin. Do not eat breakfast. Test mid-morning and prior to lunch.

If your basal dose is correct, your BS by lunchtime should be within approx.10% of what it was when you got up.

If not take more or less basal insulin – never adjust by more than 2 units up or down.

Repeat the ‘miss breakfast’ test at least 3 days hence, to see if it’s right. Keep repeating this until it is more or less right!

Make sure you are happy that that bit is right, then next do the same again but miss lunch. Your pre-lunch and pre-dinner readings should be similar now.

Then do exactly the same pre-dinner, missing dinner – and pre-bed.

Then move on to overnight.

Night time

Test before bed (as normal), take any pre-bed medications, including long-acting insulin, if that’s when you take it. Do not eat and do not take any fast acting insulin.

Ideally you would set your alarm-clock to go off every 2 hours and test your BS and record it every time throughout the night.In practice set it once to go off between 2.30am and 3.15am. Test when it wakes you and (hopefully!) go back to sleep till your normal time. Test again then (as normal)

Your BS now should be roughly similar to what it was last night. If it isn’t – what happened at 3 am? Is there too much insulin or not enough? Is that because your dose is too high or too low? – or has it ‘peaked’ at the wrong time for you?

To get it right you might find you have to alter the timing of your injections(s) instead of – or as well as – changing the actual amount of insulin you take.

Don’t worry about trying to ‘fine tune it’ – that should come later once you are on an even keel.