Hi itscurtains
Yes your dose of 20,000 IU is meant to be a loading dose , so that you can quickly reach a more acceptable blood level of VitD3. i.e. about 3000 IU per day when averaged over a week. They have probably given you 2 or three months supply. ?
Don't worry about D2 , it is the plant form of VitD , i.e. very similar to D3 , although it is thought not to have the same beneficial effects by some researchers. Some think it is less absorbable. The jury really is out on that question at the moment. However D3 is the mammalian form, that should be what you take , it is the form you make in your skin.
You most likely have a small amount of D2 from some supplementation added to a few foods , i.e some breads made from irradiated yeast, yoghurts etc etc. They probably add D2 rather than D3 so as not to upset the sensibilities of vegetarians who would not want an animal product in an ostensibly vegetarian food . The amount of food supplementation is tiny when compared to your overall vitamin D requirement. UV Irradiated mushrooms are sold in some countries , resulting in quite high levels of D2, but not in the UK , as far as I know.
D3 is made from sheeps wool ..! mostly. Although it is available from lichen, for vegetarians purposes.
When you have finished your course , you should be aware of your levels, don't just let them drop to your pre-treatment level. They will do that , IF you don't continue taking some , or go out in the sun , without suncream for a period. Don't burn , EVER , but sunlight on your skin is the best way to build up or maintain your Vitamin D level.( If possible ) Here in the UK , you cannot make Vit D from sunshine between mid-Oct and mid-April, because UVB radiation is absent from sunlight over winter. UVB is only present when the sun is high in the sky , when your shadow is shorter than you. i.e. when the sun's elevation is above 45 degrees. Which generally means between about 11 and 3 in the summer months. Direct sunlight , onto the skin will produce the maximum amount of Vitamin D in 20 mins. After that , cover up , don't burn. etc. A full body exposure in direct sun for 20 mins , will make about 10,000 to 20,000 IU of vitamin D in your skin. if you are white skinned. If you are darker skinned , then you will require longer , up to 3 to 5 times longer in order to make the same amount of Vitamin D. Melanin skin pigmentation acts as a sunscreen.
You asked what level your blood level should be , well there is disagreement about that worldwide. 50 was considered sufficient , and still is considered that by many , however just recently many in the medical profession say that 75 is better. But many Vitamin D researches say that 100 to 150 is the level you need for optimum health. As a primate species , originating in Africa , subject to strong sunlight , year round, our natural level is 120 -140. Your physiology evolved in that sunlight , with that level. All other primates have that level. You should probably aim for that yourself. Healthy , outdoor living humans achieve it , although not many UK people do . We commonly have levels 30 – 70 , depending upon season , time spent indoors , clothes, suncreams etc. That is why many people are deficient.
Well , best of luck with your treatment. I presume you have had some symptoms of Vit D deficiency ?
If you are interested in how others were treated , their responses to it , and generally more information , then have a look at this thread. It is quite long , but lots of information.
www.mumsnet.com/Talk/general_health/2421492-Vitimin-D-can-it-have-this-effect.
I have posted quite a bit here on Mumsnet , about VitD , search my nick for more info.
PS. In my opinion you might need a daily dose of around 2000 - 4000 , to keep your blood level , at least above 100, if you are in the UK , and do not get much sunshine. We all have different responses to supplementation. For any of us with a higher BMI , then because Vit D is lipid soluble we may need more. It is always a good idea to check your level, say in late March or early April to make sure that your supplementation is working. You can get a check at this NHS lab , by post. Send them a blood spot on blotting paper. They do charge , £28, if it is not requested by a doctor. www.vitamindtest.org.uk/
Hope this is helpful for you
BTBH