Vitamin D a group of fat-soluble prohormones originally known as a cure for the bone disease Rickets when it became clear that the disease was caused by vitamin D deficiency. Today we’re aware of its importance and how deficiency can play a part in many diseases.
For my Swedish readers I highly recommend this interesting YouTube-lecture by Mats Humble, in which he goes more in-depth about vitamin D.
15-30 minutes in strong sun is enough to get the recommended amount but in Sweden and northern countries this is only possible during the summer. It’s difficult to estimate how common vitamin D deficiency is but a study by Lisbeth Nordström found that 82% of adolescents in northern Sweden had vitamin D deficiency. Another Swedish study made in Göteborg found that 62% of the children participating in the study suffered from vitamin D deficiency.
Health benefits from vitamin D
In contrast to some other supplements, such as caffeine, vitamin D is more about avoiding deficiency than getting an extra boost. Low vitamin D levels are associated with some cancers, increased risk of viral infections, tuberculosis, severe asthma, depression, osteoporosis, autism, etc. while supplementation has been shown to improve performance and reduce injury occurrence, increase testosterone levels, improve osteoarthritis of the knee and much more.
I’m expecting to see more results like this as research on vitamin D continues but it’s already obvious that a sufficient level of vitamin D is extremely important for our health.
Risks of overconsumption
Like everything else, to much is never a good thing and high levels of vitamin D is potentially toxic. One article published in AJCN notes that all cases of vitamin D toxicity involve intake of ≥1000 μg (40 000 IU)/d and that it’s probably safe with levels up to 10 000 IU.
Another article published in 2012 consisting of a detailed literature search states:
Because long-term daily intakes up to and including 10 000 IU of vitamin D do not produce signs or symptoms of vitamin D toxicity and are safe for the entire general population of otherwise healthy adults, even daily vitamin D intakes of 2000 IU allow for the often-cited and excessively conservative five-fold safety factor.
Recommended daily intake
National Food Administration in Sweden (Livsmedelsverket) currently have a recommended daily intake (RDI) of 10 μg (400 IU) for adults based on old research about bone health. Later research acknowledges that this isn’t enough and most studies today supplement with 2000 IU.
In addition to sun exposure, one study noted that BMI were a significant predictor for reaching a satisfactory level. Meaning; if you’re bigger you’ll need a higher intake of vitamin D.
Generally, I’d say 2000 IU is a good level for most women and 4000 IU for most men but, as I’ve mentioned, it depends on multiple factors. Personally I prefer vitamin D from Star Nutrition which contain 2000 IU per tablet so I take two tablets daily (4000 IU) during winter.