I agree with everything Scuba has noted in his post to you. I would like to point out that the difference in measurement of D3 is crucial when trying to follow the 'guidelines', which Scuba also pointed out is the lowest level you can have before risking development of rickets!
From what I understand 40 mol/L(nmol per litre) is not 'slightly' low, it is according to some research, very likely verging on deficiency. Your result from last week at 178 nmol per litre -again from what I have read - is not considered by some to be 'too high' at all and certainly does not put you at risk of toxicity!
To convert nmol/L (your measurement) to ng/ml divide by 2.5.
So your D3 level is currently at 175 nmol/L divide that by 2.5 and your result is 70 ng/ml, which to many researchers or forward thinking doctors on this subject, is a good level, if not yet at optimal.
It depends who your read/listen to. Scaring people with possible D3 toxicity is to my mind irresponsible without giving the context of what toxic levels are. Toxicity is very rare and difficult to achieve...see another post I made on a different thread.
Snip from another thread -
It is highly unlikely that you will 'overdose' ... D3 toxicity is extremely rare and would mean taking excessive amounts over a very long period. For the worried/cautious amongst us, please see this publication, by Michael F. Holick, PhD, MD, Section of Endocrinology, Diabetes and Nutrition Department of Medicine Boston University Medical Center Boston, MA, which discusses the topic of D3 toxicity.
".......The evidence is clear that vitamin D toxicity is one of the rarest medical conditions and is typically due to intentional or inadvertent intake of extremely high doses of vitamin D (usually in the range of >50,000-100,000 IU/d for months to years...."
Why convert your measurement? Because most of the research that I have read on optimal levels (not medically conservative 'status quo' levels) uses ng/ml which is a much small amount of plasma -per millilitre instead of per Litre. Here lies confusion and the apparent cautious (scared for no reason) attitude of some members of the medical profession who are not expert or even basically educated in nutrition and or vit/min supplementation.
It is entirely up to you who you listen to.
My own choice is to keep my D3 levels at or above 100ng/ml (which is equal to 250 nmol/L) I do this by reading not only as much as I can on the subject of optimal nutrition, but by also 'listening' to my body and then making my own decisions. I feel better on so many levels when I keep D3 at an optimal level for myself as an individual. Age, weight and general health can effect what works best for any individual.
It is your choice, but my advice is to keep your level well above the current minimum recommendations. So your current 175 mol/L is much better than your previous low level. Read as much as you can and make your own decisions.