Update on vitamin D and calcium Prof Moira O’Brien 26 Feb 2010
Osteoporosis Supplement: Prof Moira O’Brien discusses the growing awareness of vitamin D as being essential to bone health and its necessity in the adequate absorpotion of calcium, as well as the most current research on calcium supplements
In the last decade, the increasing importance of vitamin D to health, especially bone health, has been highlighted in several reports. It was for example part of Recommendation 4 of the European Osteoporosis Consultation Panel in 1998.
In 2004, the US Surgeon General issued the first-ever report on bone health and osteoporosis and he especially emphasised the importance of vitamin D, stating that vitamin D is necessary for adequate absorption of calcium. There may be inadequate amounts of vitamin D in the diet, and supplementation is necessary when dietary intake of vitamin D does not meet the body’s requirements.
The European Summit on ‘The Role of Vitamin D in the Management of Osteoporosis: A MetaForum’, which was held on 10-11 October 2005 in Dublin, also emphasised the importance of vitamin D in the prevention and treatment of the bone-thinning conditions osteopenia and osteoporosis.
More recently, in October 2009, the Comité Permanent des Médicines Européen, CPME (Standing Committee of European Doctors) adopted the Vitamin D Nutritional Policy in Europe, which stated: “It is now also known that the vitamin D endocrine system is not only important for bone and muscle health, but also influences many other tissues such as the immune system, the cardiovascular/metabolic system, cell proliferation and cancer.”
This is based on well-documented biochemical, cellular and animal data generated in many research laboratories around the world. The greatest risk for bone and several major diseases and preventable health conditions are associated with 25(OH)D levels below 50 nmol/L.
Optimal bone health
Calcium and vitamin D are essential for optimal bone health and for the prevention and treatment of osteoporosis, particularly in housebound elderly. Bone is a major store of calcium and phosphate. Oestrogen is needed to form vitamin D and it is low in premenopausal women with amenorrhea, particularly in those women who are suffering from eating disorders.
Thin postmenopausal women, especially if they had an early menopause, are also at risk. Vitamin D is needed to help the body absorb calcium and is important for muscle function and the prevention of falls.
Vitamin D inadequacy is widespread worldwide, regardless of geographical location or season. Low levels of vitamin D occur in all age groups who do not get sufficient vitamin D from sunlight or diet.
Serum concentration of 25(OH)D, the main circulating metabolite of vitamin D, has been accepted since 1997 by the Panel on Calcium and Related Nutrients of the Food and Nutrition Board (IOM–NAS) as the correct functional indicator of vitamin D status. The normal level is 50 nmol/L.
There is no consensus on vitamin D inadequacy, but a Serum 25(OH)D concentration of <30 nmol/L has been suggested as an indication of vitamin D inadequacy. Vitamin D deficiency is below 20nmol/L. In some countries, over 50 per cent were below 50nmol/L, and in some, values below 20nmol/L were common.
Severe vitamin D deficiency causes rickets or osteomalacia (depending on the age of the subject and the status of the growth plate) or osteopenia or osteoporosis.
Low levels of vitamin D may be due to low oestrogen levels, low vitamin D intake and also to poor absorption due to gastrointestinal disorders, particularly gluten intolerance. We must identify and treat the causes of vitamin D insufficiency.
Vitamin D production is affected by season, latitude, duration of exposure, sunscreen use, skin pigmentation and the ability of the skin to form and process vitamin D. The major source of vitamin D is from the action of sunlight on the skin. About 15-20 minutes of sunlight a day on the face and arms during the summer helps to increase vitamin D levels.
The amount formed depends on the age of the person and the amount of sunblock used. It is very important to avoid over exposure, which results in sunburn, as we are all aware of the damaging effects of the sun also (especially skin cancer).
Reasons for the high prevalence of vitamin D inadequacy in postmenopausal women may be the result of a lack of sunlight exposure, poor nutrition and less efficient synthesis of vitamin D in the skin. With age, there is a lower amount of vitamin D precursor 7-dehydrocholesterol in the skin.
Dietary intake is a minor source of vitamin D, providing ?100 IU/day. Vitamin D is rare in foods other than fatty fish, eggs and supplemented dairy products. Even vitamin D-fortified dairy products in some countries may not contain levels indicated on the label. Vitamin D can be supplied as calcium and vitamin D preparations, multi-vitamins and supplements.
Supplements containing vitamin D alone are not readily available. Patient compliance with supplementation therapy is poor.
Inadequate calcium intake and inadequate levels of vitamin D are risk factors for osteopenia and osteoporosis. Primary prevention of osteoporosis starts early in life, in utero, and continues throughout life.
As well as a balanced diet and daily weight-bearing exercise, normal hormones, adequate caloric intake, calcium and vitamin D are essential for the prevention of osteoporosis. People taking calcium supplements must have an adequate fluid intake. We must identify those at risk.
Vitamin D is essential for calcium absorption and bone health. Prolonged low levels of vitamin D may lead to sub-optimal calcium absorption, which may increase the levels of parathyroid hormone, i.e. secondary hyperparathyroidism, with a high bone turnover and an increased risk of fractures, especially in older people (?65 years) living in nursing homes and those with osteoporosis.
Low levels of vitamin D will also increase the risk of falls and, as a result, the risk of fractures. Serum 25(OH)D levels and serum parathyroid levels should be carried out to determine whether there is a primary parathyroidism or if it is secondary due to low vitamin D Levels.
Vitamin D is an Essential part of osteoporosis management (Lim S-K et al. 2005, Heaney RP 2000). Vitamin D supplementation has been shown to reduce the risk of fracture and falls and improves muscle function in the elderly, and the efficacy of prescription osteoporosis treatments is maximised by ensuring that patients get enough vitamin D and calcium. Vitamin D is a safe and simple addition to effective osteoporosis treatment.
Many patients reported that their physicians had never explained the essential role of calcium and vitamin D supplements in their osteoporosis management.
Vitamin D supplementation must be sufficient to ensure that 25(OH)D reaches the threshold level, 50nmol/L, otherwise it will not confer the desired benefit. It has been suggested that 1,000mg of calcium and 800iul per day are required.
It can be obtained from a litre of supermilk, which is available either as low- or full-fat milk. Medically approved prescription medications such as OsteofosD3 (a once-daily drink, orange flavour), Calcichew D3 forte (twice-daily chewable tablet, lemon flavour), Ideos (twice-daily, orange flavour), Calvidin (twice-daily chewable tablet), Caltrate Plus (once- or twice-daily tablet, swallow or chew) are also available.
Calcitriol is a vitamin D analogue. It is licensed for the treatment of established post-menopausal osteoporosis. Patients should have serum calcium and creatinine monitored for hypercalcaemia.
Defining the upper limit of vitamin D intake, the Food and Nutrition Board has declared 2,000 IU/day as an acceptable upper limit for vitamin D intake. It is likely that chronic exposure to substantially higher levels would not cause harmful effects. No toxic effects have been observed in individuals who were given 4,000 IU/day.
Vitamin D toxicity with hypercalcemia is generally accompanied by Serum 25(OH)D level 200 nmol/L. Daily vitamin D intake >40,000 IU is required to achieve this level.
Vitamin D is synthesised in the skin via the conversion of 7-dihydrocholesterol by ultraviolet B light and heat.
Once formed in the skin (or absorbed in the gut from dietary sources), vitamin D is hydroxylated in the liver to 25-hydroxy vitamin D 25(OH)D, the major circulating metabolite of vitamin D and the most reliable indicator of vitamin D status. 25(OH)D is subsequently metabolised in the kidney to the active form of vitamin D, 1,25-dihydroxyvitamin D 1,25(OH)2D.
Production of 1,25(OH)2D is enhanced by parathyroid hormone (PTH) and serum calcium and phosphate.
Prof Leif Mosekilde (Aarhus University Hospital, Denmark) at the Metaforum in 2005, pointed out that other tissues also have the capacity to produce 1,25(OH)2D locally. Approximately 80 per cent of vitamin D in the body is from endogenous production, with about 20 per cent from exogenous sources (diet and supplements).
Vitamin D is an essential part of osteoporosis management.
Almost everyone should get vitamin D as part of their treatment, alongside an effective prescribed anti-osteoporotic medication. Vitamin D has a good safety profile.
Supplementation with vitamin D and calcium should be done with caution in individuals with renal insufficiency. High-dose supplementation carries a risk of hypercalcaemia with subsequent impairment of kidney function.
Special caution is also required in the treatment of patients with cardiovascular disease as the effect of cardiac glucosides may be accentuated by supplementation with vitamin D and calcium.
l Prof Moira O’Brien, FRCPI, FFSEM,FFSEM. FTCD.