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This page helps you to understand blood test results for Vitamin D and gives you the reference range to determine if your lab test results mean that you have high, low or normal Vitamin D levels.
We outline the risk factors associated with both raised and lower Vitamin D levels.
Reference Ranges for Vitamin D:
| Measurement unit | Metric | Optimal | Borderline | Risk |
|---|---|---|---|---|
| US Conventional Units | ng/dl | 30-99 | 20-29 | <=19 or >= 100 |
| Standard International Units | nmol/L | 74 – 249 | 54-73 | <=53 or>= 250 |
What is Vitamin D
Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, and available as a dietary supplement. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis [67].
Function of Vitamin D
Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone. It is also needed for bone growth and bone remodelling [68,69]. Without sufficient vitamin D, bones can become thin, brittle, or misshapen [67].
Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation [67,68,69]. Some studies also report that Vitamin D plays a role in regulating estrogen and testosterone levels in males and females [81].
Risk factors associated with Vitamin D
- Osteoporosis is most often associated with inadequate calcium intakes, but insufficient vitamin D contributes to osteoporosis by reducing calcium absorption [72].
- Rickets and osteomalacia are extreme examples of the effects of vitamin D deficiency.
- A growing body of research suggests that vitamin D might play some role in the prevention and treatment of type 1 [73] and type 2 diabetes [74], hypertension [75], glucose intolerance [76], multiple sclerosis [77], and other medical conditions [78,79].
- Vitamin D toxicity due to excess Vitamin D is rare, but can cause non-specific symptoms such as anorexia, weight loss, polyuria, and heart arrhythmias [67]. More seriously, it can also raise blood levels of calcium which leads to vascular and tissue calcification, with subsequent damage to the heart, blood vessels, and kidneys [68].
Notable variations by demographic group
Although there are some areas of debate in relation to vitamin D requirements and the impact of vitamin D intake on many aspects of human health, there is a general agreement that prevention of vitamin D deficiency is a public health priority. There is concern that low status appears to be prevalent, particularly in older adults and in some ethnic groups particularly those with darker skin [80].
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Diet to improve Vitamin D
Oily fish such as Salmon and Mackerel contain Vitamin D. However, very few foods contain high levels of vitamin D meaning supplementation is recognised as the best way to correct a deficiency [67].
Supplements for Vitamin D
Supplementation is a common and effective way to boost levels of Vitamin D
Supplemental vitamin D is available in two forms, D2 (ergocalciferol) and D3 (cholecalciferol) that differ chemically, but are similarly effective at boosting Vitamin D levels [67].
If Vitamin D levels are above the accepted range then supplementation should cease until levels come back into range [67].
Exercise to improve Vitamin D
Research from the Harvard School of Public Health suggests that three or more hours a week of vigorous exercise leads to a moderate increase in levels of vitamin D [82].
Sleep for Vitamin D
Low Vitamin D is associated with poor sleep, and supplementation can improve sleep quality [83]. However there is little evidence to suggest that targeting sleep will increase vitamin D in the body.