Vitamin D - How Much Do We Need?

Vitamin D has been a hotly debated micronutrient over the last few years.  Current dietary recommendations as set by the Institute of Medicine are that adults up to 50 years of age require 200 International Units (IU) per day, that adults 51 - 70 years of age should obtain 400 IU per day, and adults over 70 years of age should get 600 IU per day.  For purposes of safety the Institute of Medicine has set a tolerable upper level intake at 2,000 IU per day.  Since these recommendations were set, science has continued to explore the health benefits of vitamin D with many of these studies suggesting that much higher doses of vitamin D are needed to achieve health benefits beyond meeting basic nutritional requirements.  The weight of the evidence for a higher daily recommendation has led the Institute of Medicine to re-evaluate their recommendations for dietary vitamin D with a final report due to be released in the very near future.

In an attempt to provide relevant data for the re-evaluation of dietary vitamin D recommendations, a new vitamin D research study aimed at determining the appropriate amounts of vitamin D for health benefits and safety was conducted.  For their assessment of vitamin D the nutrition researchers analyzed previously published research trials on the potential benefits of vitamin D for fractures, falls, heart health, and cancer and on the safety of vitamin D at high doses.  The results of this data analysis showed:

• Fractures - Doses of vitamin D between 482-770 IU per day reduced the risk for non-vertebral fractures by about 20% and reduced the risk for hip fractures by about 18%.  Lower doses of vitamin D did not reduce fracture risk.  Optimum fracture prevention occurred with blood levels of vitamin D between 75-110 nmol/L (30-44 ng/ml).
• Fall Prevention - the risk of falling was reduced by 19% when vitamin D was consumed at doses of 700-1,000 IU per day, while lower doses did not reduce the risk of falls.  Optimum fall prevention was observed when blood levels of vitamin D were between 75-100 nmol/L.
• Non-Skeletal Endpoints - data collected and analyzed from studies on the impact of vitamin D on cancer, heart health, hypertension, and overall mortality suggest that optimum benefits were achieved with a blood level of vitamin D around 100 nmol/L.
• Safety - Elevated calcium levels are typically used to measure vitamin D toxicity.  According to this new report, vitamin D intake up to 100,000 IU per day or blood levels up to about 640 nmol/L had no effect on average blood calcium levels.  While a handful of individual case reports of elevated calcium were identified, all the relevant cases occurred at vitamin D blood levels higher than 500 nmol/L.

This is an important study that might well influence new dietary recommendations for vitamin D.   According to these study results, an optimum blood level of vitamin D for a range of health benefits is between 70-110 nmol/L.  The study investigators indicated that this level can be obtained by consuming between 1,800-4,000 IU vitamin D per day.  This daily consumption amount is substantially higher than the current upper limit of 2,000 IU per day as set by the Institute of Medicine.  However, based on the data from this study, doses much higher than this had no toxicity.  In those cases where elevated calcium was observed, blood levels of vitamin D were 4 to 5 times higher than the optimum levels.  Based on these study results, consuming 1,800-4,000 IU per day appears to have numerous health benefits with little or no risk of toxicity.

In addition to the health endpoints examined in this study, a previous study has suggested that vitamin D might support weight loss. In this study, a vitamin D blood level of 30 ng/ml was associated with a weight loss of about 12 pounds.  A blood level of 30 ng/ml is equivalent to 75 nmol/L and is thus within the optimum range defined by the latest study.

According to this latest study, consumption of 400-800 IU per day leaves about 50% of the adult population with below-optimum blood levels of vitamin D.  It will be interesting to see if the Institute of Medicine changes their recommendation for vitamin D intake and if so to what level. 

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