In late 2008 I was diagnosed with relative deficiency of D3 with a reading of 65 nmol/L, serum levels of greater than 75 nmol/L indicate sufficient D3 levels according to the lab report, all other bloods were fine.
I read extensively and found defiecency of D3 to be linked with these issues I have -- weight loss resistant, T2, endometriosis, a malignant melanoma. I settled on D3 drops taking 4000 iu daily for about 6 months then upped it to 10,000 iu daily. After 12 months I was retested with all my regular bloods and D3 was now 170 -- desired range is up to 140 ! Slightly heavy handed dosing so I scaled it back to 4000 iu a day.
I know that a greater proportion of Australians over 55 years of age are found to be deficient in D3. I arrived in Australia from the UK as an 18 year old in 1970, fair skinned, burnt easily so avoided exposure and used sunscreen liberally. My husband tans easily, swims and wears shorts all summer and basically gets good exposure to sunlight. He too read the research and having impaired FBGs decided to supplement at 4000 ius a day. After a year he asked for a test and was found to be at the lower end of the sufficient range. That is after 12 months of supplementing and sun.
Daughter aged 30 was found to have 'on the floor' levels of D3. She too is fair skinned, works outdoors, suffers from clinical depression, anxiety attacks. Supplemented at the rate of 4000 ius and is in the good range now.
She and I now find we are able to tolerate quite a reasonable amount of time in the sun (three hours of tennis) without sunscreen and do not burn. For the first time in my 59 years I had a summer tan!! Perhaps we lose our ability to absorb D3 as we age. I also think that I inherited low D3 from my mother and I in turn possibly passed on low levels in my children by being deficient during my pregnancies. Will probably never prove this but that is my theory.