Vitamin D supplements will help reduce bone loss, fractures and disease
(Aotea News, May 2010)
By Michael Crooke
Aotea Pathology and doctors generally are concerned by evidence showing widespread vitamin D deficiency in people in New Zealand. For older people this is contributing to bone loss and consequent fractures, and in the general population there may be increased risk of a range of serious diseases.
Our advice is that providing vitamin D supplements is a safe, cost-effective and, indeed, necessary treatment.
Supplements instead of testing for asymptomatic, at-risk people
Measuring vitamin D is comparatively expensive and it is reasonable to provide supplements to asymptomatic, at-risk people without testing. In fact, routine testing of vitamin D levels is not usually necessary before or after starting vitamin D supplementation.
Sunlight important but insufficient in winter
The Cancer Society agrees that there is benefit from moderate exposure to sunlight during summer, but sunburn must be avoided. Sufficient vitamin D to reach optimal levels can be made by exposing the hands, arms and face for a few minutes each day.
Prolonged sun exposure during the summer will not provide the body with sufficient vitamin D for throughout the winter. It will, however, increase the risk of skin cancers. Autumn is a good time to get out in the sun and to top-up vitamin D levels, as the sunburn risk is lower.
It is estimated that 50–80 per cent of New Zealand’s population has vitamin D insufficiency in winter, because of our southerly latitude. There is almost no vitamin D produced by sunlight between May and September.
Who is at most at risk of severe vitamin D deficiency?
Vitamin D and calcium supplementation is appropriate for people at high risk who cannot increase their sun exposure.
- older people in residential care
- older people admitted to hospital
- patients with hip fracture
- dark-skinned men and women (particularly if veiled)
- mothers of infants with rickets
- people unable to get regular sun exposure.
Recommendations for supplementation
To achieve the recommended level of at least 50nmol/L in winter, supplementation is, ideally, required for everyone.
For most people, this is best achieved by taking 1.25mg vitamin D3, 50,000 units as a once monthly dose from May until September.
There is no need to measure vitamin D first in most people as they will be insufficient during winter.
There is no need to check levels after the standard dosing as this will raise most people to sufficient levels and there is no danger of toxicity.
Measurement may be considered in high-risk people as very low levels may dictate more aggressive replacement.
Supplementation reduces the risk of fractures in the elderly, particularly those in institutions, but must be combined with an adequate calcium intake.
What is the risk of toxicity with excessive supplementation?
The current recommended daily dose is only half the amount in a teaspoon of pure cod liver oil and is insufficient to provide optimal levels!
There has been extreme caution in recommending supplements containing higher doses of vitamin D because of misplaced concern about toxicity.
Recent literature suggests a ‘no adverse effect’ limit of 50 ug or 2000IU daily, but this is probably much lower than the toxic dose.
Toxicity has never been observed at blood levels <220nmol/L and in most cases with clear hypercalcaemia, levels have been over 600nmol/L.
10,000 units daily produces levels only around 140nmoL/L and most documented toxicity has involved doses of more than 1000ug daily, that is, 40,000IU.
Are there benefits of vitamin D apart from bone health?
Vitamin D has a wide range of biological actions apart from the well-known effects on calcium and bone metabolism.
Although there is not yet absolute evidence of causation in other diseases, the associations are strong and it seems prudent to maintain levels at least above 50nmol/L and probably above 75nmol/L.
- Brain, prostate, breast and colon tissues, as well as immune cells, have a vitamin D receptor.
- 25OH vitamin D controls over 200 genes, including those responsible for cellular differentiation, apoptosis and angiogenesis.
- It is also immunomodulatory, promoting activity of macrophages and monocytes.
- There are effects to increase production of insulin and inhibit synthesis of renin.
- Prospective and retrospective studies indicate that levels of 25OH vitamin D below 50nmol/L are associated with a 30—50 per cent increased risk of colon, prostate and breast cancer.
- There has been no controlled trial but data suggest that those with intake of 250—600 units/day have about half the risk of colorectal cancer as those with an intake under 100 units/day.
- There is similar data for breast cancer.
- In a study of men with prostate cancer, those who worked outdoors developed the disease three to five years later than indoor workers.
- Vitamin D deficiency has also been linked to schizophrenia, depression, hypertension lung function, wheezing illnesses, polycystic ovarian disease, menstrual problems and infertility.
When testing is appropriate
Vitamin D testing is appropriate for:
- unexplained raised serum alkaline phosphatase or low calcium or phosphate
- atypical osteoporosis
- unexplained proximal limb pain
- in older people
- unexplained bone pain, unusual fractures
- or other evidence suggesting metabolic bone disease (consider specialist advice for people in this category).
If there is clinical suspicion of severe symptomatic vitamin D deficiency it is appropriate to investigate with serum calcium, phosphate, alkaline phosphatase and vitamin D levels plus other tests as indicated.
Specialist treatment is recommended for people identified as having metabolic bone disease other than simple vitamin D deficiency. 25-hydroxyvitamin D is almost always the most appropriate measure of vitamin D status.
Measurement of 1, 25-dihydroxyvitamin D is rarely required – it is very expensive and results do not provide a good reflection of vitamin D status. It is not available in New Zealand and specimens will be sent overseas for analysis only after written justification from a relevant specialist and discussion with a pathologist.
This article includes information from the Best Practice Advocacy Centre NZ document BNP, Haemochromatosis and Vitamin D Testing in Primary care, which can be read online in this BPAC document.