Health Bulletin-February 2016

Vitamin D and health

My 15-year old daughter recently visited a pediatrician for annual physical checkup. Following the examination, the doctor gave a routine prescription for blood testing, including a lipid profile, glucose and several others. However, it did not have the test for Vitamin D levels. Following my request, the doctor included a test for Vitamin D, as well. After a couple of days, when the test results came in, the doctor was surprised to find how low were my daughter's Vitamin D levels (8 ng/mL) and promptly recommended 2000 IU dose per day.

Until recently, there has been little interest in the medical and pediatric communities regarding the vitamin D status of their patients. It had been assumed that everyone was vitamin D sufficient and that only those patients with fat-malabsorption syndromes were at risk [1]. Even today, not all physicians check the status of Vitamin D levels in children and young adults. Risk factors for vitamin D deficiency are premature birth, skin pigmentation, low sunshine exposure, obesity, malabsorption and advanced age [2, 3].

Epidemiologic evidence and prospective studies have linked vitamin D deficiency to increased risk of many chronic diseases including autoimmune diseases, cardiovascular disease, deadly cancers, type II diabetes and infectious diseases [4, 5]. Evidence for vitamin D's important role in health is based on observation that all tissues and cells in the body have a vitamin D receptor, and thus respond to the active form of vitamin D [5, 12].

Without vitamin D, 40% and phosphorus absorption to >80%. Vitamin D deficiency ultimately leads to removal of precious calcium reserves from the skeleton and loss of phosphorus in the urine. In adults, vitamin D deficiency and secondary hyperparathyroidism increases loss of mineral and matrix, which can cause osteopenia (low bone density), osteoporosis (weak, brittle bone) and increased risk of fracture. In addition, as in children, vitamin D deficiency causes a mineralization defect of the osteoid (matrix used in bone formation) leading to osteomalacia (softening of bone). Unlike osteoporosis which is a silent disease, osteomalacia can cause throbbing bone pain and muscle weakness that is often misdiagnosed as fibromyalgia, chronic fatigue syndrome, or simply the patient is written off as being depressed [5].

Vitamin D deficiency causes muscle weakness. Skeletal muscles have vitamin D receptor and may require vitamin D for maximum function. Multiple clinical trials in elderly women demonstrate reduction in fractures with vitamin D supplements [6]. For pre-menarcheal girls, daily vitamin D intakes showed improvement in bone density and muscle mass. In another randomized trial in children during winter, daily vitamin D supplementation lowered the risk of influenza A and the incidence of asthmatic attacks. Another clinical study involving patients with multiple sclerosis provided an evidence of benefit in lowering relapse rates and severity scores of multiple sclerosis. A study conducted with a group of women revealed a correlation between elevated vitamin D levels and reduction in cancer diagnosis [4].

Vitamin D sources

The vitamin D deficiency/insufficiency epidemic is caused by the fact that few foods naturally contain or are fortified with vitamin D. Exposure to sunlight is the best way to obtain optimal levels of Vitamin D. The skin has a huge capacity to produce vitamin D and the vitamin D that is produced in the skin lasts 2-3 times longer in the circulation when compared to the vitamin D that is taken as an oral supplement. Exposure of arms and legs for 5-30 minutes to sunlight (depending on time of day, season, latitude, and skin pigmentation) between the hours of 10 a.m. and 3 p.m. twice per week is often adequate [5]. The concentration of vitamin D in cow's milk is roughly 35-70 IU per quart [7]. These are rather low levels of vitamin D from the perspective of maintaining optimal levels as recommended by the Food and Nutrition Board of the Institute of Medicine in 2010 [13]. Accordingly, the business practice of supplementing cow's milk with chemically synthesized vitamin D was initiated. In present day, almost all milk sold commercially in the United States has 400 IU of chemically synthesized vitamin D added per quart [8]. A diet high in oily fish also prevents vitamin D deficiency.

Vitamin D, consumed as the supplement vitamin D3, is technically not a hormone and is not biologically active. Once vitamin D is made in the skin or ingested in the diet it must first be metabolized to 25-hydroxyvitamin D [25(OH)D], which is considered to be the major circulating form of vitamin D that is measured to determine a person's vitamin D status. However, 25(OH)D is also biologically inert and is converted to 1,25-dihydroxyvitamin D [1,25(OH)2D] by the kidney. Once formed 1,25(OH)2D, the biologically active hormone, enters target tissues that regulate calcium and phosphorus metabolism [9].

Although there is no consensus among physicians on the optimal levels of 25-hydroxyvitamin D in serum, vitamin D deficiency is defined by most experts as a 25-hydroxyvitamin D level of 30 ng/mL can be considered as sufficient [11, Figure]. It is estimated that children need at least 400-1000 IU of vitamin D per day while teenagers and adults need at least 2000 IU of vitamin D per day to satisfy their body's vitamin D requirement. It is estimated that 1 billion people worldwide are vitamin D deficient/insufficient. Correcting and preventing this deficiency could have an enormous impact on reducing health costs and improving general health worldwide [5, 10].

Caution: Be aware of the quality and safety of dietary supplements, which are exempt from the strict regulatory oversight (see ATA Health Bulletin, May 2015).

References:

Holick MR (2010) The D-lemma: To Screen or Not to Screen for 25-Hydroxyvitamin D Concentrations, Clinical Chemistry 56: 729-731
Lips, P (2006) Vitamin D physiology. Progress in Biophysics and Molecular Biology, 92: 4-8
Holick MF (2011) Vitamin D: Evolutionary, Physiological and Health Perspectives, Current Drug Targets, 12: 4-18
Vieth R (2011) Why the minimum desirable serum 25-hydroxyvitamin D level should be 30 ng/ml. Best Practice & Research Clinical Endocrinology & Metabolism 25: 681-691
Holick MF (2007) Vitamin D Deficiency, N Engl J Med 357: 266-81
Vieth R. The Pharmacology of Vitamin D, Including Fortification Strategies, Chapter 61, Vitamin D, Second Edition, Editors Feldman and Glorieux
Hollis B.W., et al. (1994) Vitamin D compounds in human and bovine milk In Advances in nutritional research. Draper, H.H., Ed., Plenum Press, New York, pp. 59-75
Information on NIH website:Â https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Norman AW (2008) From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health. Am J Clin Nutr 88(suppl):491S-9S
Zittermann A (2003) Vitamin D in preventive medicine: are we ignoring the evidence? British Journal of Nutrition, 89: 552-572
Proposed by Pilz S et al. (2011) Vitamin D, cardiovascular disease and mortality, Clinical Endocrinology 75, 575-584
Holick MF (2008) The vitamin D deficiency pandemic and consequences for nonskeletal health: Mechanisms of action, Molecular Aspects of Medicine 29: 361-368
Institute of Medicine (Nov 2010): Dietary Reference Intakes for Calcium and Vitamin D