When does the basal affect my BG?

Once on this forum, someone posted that if you want your bood glucose to be lower at, say 10am, you should raise the basal beginning four hours prior to that. Never seemed quite right.

I want to know how many hours prior to a regular time period of steadily raising BGs should I up the basal. For example, woke up at 104 (8am), was 109 at 9am and 165 at 10am. Prior to that I had been hovering around 100 since 4am.

I am afraid to raise it too early, as I am trying diligently to avoid lows at wake up.

I wouldn't change it based on just one high, Spock. But if I see a regular pattern of highs in a particular "time zone" I will raise it during the period two hours prior, not four. This is what John Walsh advises.

I agree with Zoe ...2 hours prior ...and I think we need to remember also the bolus one has delivered( or not ???) ...ie did you bolus for a meal between 8 AM and 10 AM ??

The time delay before your insulin starts to reach full effectiveness can generally be considered to be the time to peak. If you use a pump and use a Humalog/Novolog/Aprida, then that would be 30-90 minutes. If you take an injected insulin like Lantus/Levemir, it is more typically 2-4 hours.

And I agree with Zoe, changing a basal should be done based on consistent average readings that are high or low. I like to look at averages over a week or even longer.

Here is the formula I use. I believe that humalog stay active in my system about 3 hours and 50 minutes. Humalog's activity profile which is provided in the leaflet with every new bottle shows that humalog activity is just about a perfect bell shapped curve. Therefore, I divide 3 hours and 50 min in half to determine that humalog reaches peak activity at 1 hour and 55 minutes. I of course round this to 2 hours for simplicity.

If I am spiking at 10 am, then I raise my 8 am basal. If your insulin stays active longer/shorter than you may need to make some adjustments. There is a certain amount of trial and error. Make an adjustment and check your BG to see if you are responding as you expected.

I agree with Zoe and nel. Raise your basal two hours before your BG rises. I would only do this if I had a rising BG trend three days in a row and a meal was not involved. You mention a BG of 165 at 10 a.m. Did you have breakfast prior to 10 a.m.? If so then you'll also need to consider the timing, quality, and dosing (I:C) for that meal. In the scenario you mentioned, it would be easiest to make a rational change if no meal were involved. Do your BG's rise in the morning if you skip breakfast?

The two hour lead time, by the way, is based on the nominal peak insulin action time of the current rapid acting insulins.

Your overnight basal rates seem to be serving you quite well.

I agree that the correct lead time is about 2 hours.

If you look in "Think like a pancreas", it shows typical basal requirements for people at different ages. I find a that series of smooth basal rate changes best matches my basal needs. The exception being a sharp increase at 3 am to combat the dawn phenomenon.

My rates are
12:00 am 0.15 u/h
03:00 am 0.50
06:00 am 0.45
09:00 am 0.40
12:00 pm 0.35
03:00 pm 0.30
06:00 pm 0.25
09:00 pm 0.20

Took me 4 years to finally settle on these rates. My FBS is usually around 90.
These rates happen to work for me because my insulin sensitivity increases all day long. But you have to experiment and find what works best for you.

This is not a one time thing--it is a "regular time period of steadily raising BGs." The advice is great and I will make the changes. Thanks!

Wow...this is such good info you all provided...great question (will be so helpful to many) and responses are fantastic..you guys/gals rock!