You get vitamin D from your food, supplements and the sun, the primary source being exposure to sunlight. Seafood provides the most dietary vitamin D. Vitamin D deficiency increases risk of Alzheimer’s disease. Supplements of vitamin D can be derived from animal or vegetable source (mushrooms and lichen). Supplementing 800iu (20mg) a day for 12 months has been shown to improve cognitive function and lessen amyloid protein markers. Vitamin D used to be thought of as only necessary for healthy bones, but is now understood to influence over 200 critical genes, supporting healthy immunity and reducing risk of numerous diseases from cancer to heart disease as well as dementia.
The Reference Nutrient Intake, assumed to be the right amount for maintaining healthy bones, is set at 10mcg (400iu). The UK government recommends that everyone should be supplemented 10mcg during the winter but the Irish authorities tell everyone to supplement 25mg (1,000iu) all year round for immune support. But is this enough?
In truth the amount you ‘need’ depends entirely on what gets your blood level up to an optimal level. The table below shows you what you want to achieve:
| Low | 30 nmol/l | 12 ng/ml or below |
| Medium | 50-74 nmol/l | 20 to 29.6 ng/ml |
| Optimal | 75-125 nmol/l | 30-49 ng/ml |
| High | 125 nmol/l or above | 50 ng/ml or above |
Vitamin D is easy to test, either through your doctor or privately, including online home-test kits. In the UK this can be done via a NHS lab – https://www.vitamindtest.org.uk. It’s well worth knowing. Alternatively, If you’re not sure what yours is and want to find out, in the UK there’s an Essential Health Check home test kit you can buy from YorkTest which is extremely good value. It also tests your serum B12, folate, cholesterol triglycerides as well as your vitamin D levels.
A major review of all bone-related studies recommends achieving a blood level of at least 50 nmol/L with daily vitamin D supplemental doses of 10 to 20mcg (400 to 800iu).
According to a major review of hundreds of studies, a higher blood concentration of 75 nmol/L is required for maximum vitamin D related disease prevention, which would require a higher supplemental intake of at least 10mcg (400iu) up to 50μg (4,000iu) closer to the level given in this study.
The variability depends on one’s dietary intake and sun exposure – since vitamin D is made in the skin in the presence of sunlight. Dietary intake means eating oily fish, milk or vitamin D enriched mushrooms and eggs. A portion of salmon or mackerel gives about 10mcg compared to white fish, which is about 5mcg. A cup of milk gives 3mcg and an egg 1mcg. Some mushrooms that are grown indoors, and exposed to light, like us, can then make vitamin D. A portion of such mushrooms could provide over 5mcg. These mushrooms are often labelled ‘high Vitamin D’. That’s about the same as half an hour sunlight a day in the summer, exposing both arms and face. This only creates about 5 to 10mcg. Exposing twice as much skin would double this so bear this in mind when in the sun.
In the summer months we’d recommend a minimum daily supplement of 15mcg (600iu) daily. Generally, in the winter months for those unable to escape to the sun, we recommend supplementing 25mcg (1,000iu) daily.
For those not eating fish, such as vegans and vegetarians, or not exposing themselves to sunlight, it would appear that supplementing 25mcg (1000iu), more than double the UK’s Reference Nutrient Intake of 10mcg, is likely to be needed to keep blood levels in the healthy range. There is no danger with vitamin D overdose at even four times these levels. Many nutritional therapists take 75mcg (3,000iu) in the winter.
Vitamin D can be stored in the body, so you can opt to take seven times the daily dose once a week.
