Vitamin D is not a vitamin but a pro-hormone, very similar in action to steroid hormones such as testosterone, DHEA, oestrogen and cortisol. It is produced by the action of sunlight on the skin, which causes cholesterol to be converted into vitamin D3.
D3 then circulates in the blood and it is further activated in the kidney and liver to a compound that is extremely important for bone health, neurological health, weight loss and the immune system. There is good evidence to suggest that vitamin D3 plays an important role in preventing autoimmune conditions such as rheumatoid arthritis, multiple sclerosis, thyroid conditions and cancer.
Unless you get a lot of exposure to sunlight or eat lots of oily fish chances are you are vitamin D deficient. The best way to find out your vitamin D levels is to get a 25(OH)D blood test. Most labs will state the <25 ng/mL is deficient, 26-50 ng/mL is insufficient and greater than 50 ng/mL is sufficient. However, prominent vitamin D researcher Dr Hollick suggests that we should get our levels up to at least 80 ng/mL. If you live north of 40-degree latitude (i.e. anywhere in the UK) the suns ultraviolet light is not strong enough to synthesise vitamin D in the skin during the winter. Even during the summer when the sun is strong enough you need to get at least 15 minutes a day of sun exposure during the height of the day to at least 25% of your body. Unfortunately most people cover themselves with sunscreen the minute they go outside so they get minimal unprotected sun exposure. Factor 8 reduces vitamin D synthesis by 97% and factor 15 reduces vitamin D synthesis by 99.9%. What might be a better idea is to get a bit of unprotected sun exposure – but don’t burn yourself – then cover up with sunscreen. The easiest way to get vitamin D will be as a supplement, thankfully vitamin D is pretty cheap – however it must be vitamin D3. The WHO recommend just 400IU a day, however that is far from enough to get your blood levels up to that magic 80 ng/mL mark. The National Health and Nutrition Examination Survey suggested a dose of 3800IU for those above a 25(OH)D threshold of 55 nmols/L and a dose of 5000 IU for those below that threshold. You can see the stark contrast between 400IU recommended by the WHO and the 4000-5000IU recommended by this research group. I would tend to go with the higher supplement recommendation. Dr Hollick suggests that to get blood levels of vitamin D3 up to the 80 ng/mL mark that you take 100,000IU – yes 100,000 IU per week for a 6-8 week period. Now instead of taking 15,000IU per day he recommends that you take a bolus dose twice a week. On a Monday you would take 50,000IU – 25,000IU in the morning and 25,000IU in the evening and repeat this again on Thursday. For some reason this bolus dose twice a week seems to boost blood levels quicker than taking a smaller dose more often. Now of course you wouldn’t start this mega dose of vitamin D3 without first getting your blood levels assessed and monitored during the 6-8 weeks.