Comparison: Human Body, Safe Nutrient Intakes and Leaky Buckets
The 3rd International Vitamin Conference ended yesterday in Washington DC. Staff from the NIH National Institute of Standards and Technology (NIST) and Office of Dietary Supplements (ODS) were actively involved in the conference. Presentations and discussions often centered on the importance of standards and robust, validated methods to accurately measure vitamins in products (e.g. foods and supplements) and biological matrices (e.g. blood, urine, biopsies). Commutability was a frequently used term. Why? Because the merging of data acquired at many laboratories using different equipment at any time requires an understanding of the equivalence of numbers derived using different analytical procedures.
It is important to know if +49% to -28% shifts in serum 25(OH)D3 concentrations reflect seasonal variation subcutaneous vitamin D synthesis from sun exposure (Cashman et al, 2014) or might be attributable to laboratory assay drift. Without robust laboratory methods and evidence that intra- and inter-assay variability is constrained, one could incorrectly conclude that vitamin levels (in something - product, blood, etc) are trending when the issue is analytical migration.
At many times during the conference, experts discussed safety concerns of excessive nutrient intakes. Because many vitamins are sensitive to oxidation and moisture, federal mandates (CFR 101.9) depend upon vitamin overages at time of manufacture to ensure labeled vitamin levels per serving at time of consumption. Overages are usually determined based on shelf life expectations and rate of disappearance.
Ultimately, nutrient status of an individual reflects dietary choices. Kang and colleagues report that dietary supplement can improve nutrient intake. And as Bailey and colleagues observed in the US, Koreans using dietary supplements also make more nutritious food choices.
People can harm themselves from repeated bad choices. Too little or too much nutrition is never optimal. For example, the health of a child may be affected for a lifetime if placental transfer of vitamin D is compromised during pregnancy. And despite high levels of sunshine in the Mediterranean regions, maternal hypovitaminosis D during pregnancy remains common. What is the safest remedy? Should foods be fortified with vitamin D? Should vitamin D supplementation be recommended? How often should a vitamin D supplement be taken? What concentration? What about vitamin A? Vitamin C? Folate? At IVC14, experts discussed the pros and cons of fortification, biofortification and dietary supplementation.
The safety/efficacy answer cannot be determined by dietary assessment alone. The nutritional status of the individual is relevant. Consider vitamin D. In vitamin D deficient pregnant women (< 20.5 nmol/L), supplementing with 4000 IU vitamin D3 daily for up to 16 weeks was safe and the most effective dose to achieve serum 25(OH)D3 levels above 80 nmol/L. Whereas, 1,000 IU vitamin D3 daily is sufficient to maintain serum 25(OH)D3 concentrations of 80 nmol/L in New Zealand men and women during the winter (Logan et al, 2012). In a similar fashion, the kinetics of docosahexaenoic acid (DHA) metabolism in healthy older individuals depends upon circulating omega-3 [eicosapentaenoic acid (EPA) and DHA] concentrations (Plourde et al, 2014).
Our bodies are like a bucket with a hole in the bottom. Optimal nutritional status can be conceptualized as keeping a leaky bucket full, or nearly full with water (nutrients). When the bucket is almost empty or the hole in the bottom is large, water (nutrients) have to be added at a rate to overcome the loss and faster if the goal is to fill the empty void. There is little concern about adding water (nutrients) too fast until the bucket is nearly full. Like a bucket, a safe nutrient intake is a function of pool size (bucket), rate of consumption (intake), and metabolism (leakiness).
Cashman KD, Kinsella M, Walton J, Flynn A, Hayes A, Lucey AJ, Seamans KM, Kiely M. The 3 epimer of 25-hydroxycholecalciferol is present in the circulation of the majority of adults in a nationally representative sample and has endogenous origin. 2014 J Nutr doi: 10.3945/jn.114.192419
Kang M, Kim DW, Baek YJ, Moon S-H, Jung HJ, Song YJ, Paik H-Y. Dietary supplement use and its effect on nutrient intake in Korean adult population in the Korea National Health and Nutrition Examination Survey IV (2007-2009) data. 2014 Eur J Clin Nutr doi: 10.1038/ejcn.2014.77
Bailey RL, Fulgoni II VL, Keast DR, Dwyer JT. Dietary supplement use is associated with higher intakes of minerals from food sources. 2011 Am J Clin Nutr doi: 10.3945/ajcn.111.020289
Karras SN, Anagnostis P, Annweiler C, Naughton DP, Petroczi A, Bili E, Harizopoulou V, Tarlatzis BC, Persinaki A, Papadopoulou F, Goulis DG. Maternal vitamin D status during pregnancy: the Mediterranean reality. 2014 EJCN doi: 10.1038/ejch.2014.80
Dawodu A, Saadi HF, Bekdache G, Javed Y, Altaye M, Hollis BW. Randomized controlled trial (RCT) of vitamin D supplementation in pregnancy in a population with endemic vitamin D deficiency. 2013 JCEM doi: 10.1210/jc.2013-1154
Logan VF, Gray AR, Peddie MC, Harper MJ, Houghton LA. Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months. 2012 Br J Nutr doi: 10.1017/S0007114512002851
Plourde M, Chouinard-Watkins R, Rioux-Perreault C, Fortier M, Dang MTM, Allard M-J, Tremblay-Mercier J, Zhang Y, Lawrence P, Vohl M-C, Perron P, Lorrain D, Brenna JT, Cunnane SC. Kinetics of 13C-DHA before and during fish-oil supplementation in healthy older individuals. 2014 Am J Clin Nutr doi: 10.3945/ajcn.113.074708