September 2015 Health Bulletin

How much Vitamin D is enough?

There has been substantial controversy as to what level of vitamin D in the blood is required for bone and muscle health. Some experts propose that a healthy level of Vitamin D is 50 nmol/L (20 ng/mL) or above while others say that people should have a level of 75nmol/L (30 ng/ml) or more. The Institute of Medicine in the USA have proposed 50nmol/L or above as vitamin D sufficiency. This issue has been addressed in a study published in JAMA, August 20151.

The researchers recruited postmenopausal women aged up to 75 years who did not have osteoporosis, as defined by a bone density test, who had a vitamin D level between 14 and 27 ng/ml (35- 67 nmol/L). They chose an upper limit below 75nmol/L to allow for measurement error and therefore not to include women with levels above 75 at the start of the study.

The women were randomly allocated to take placebo, low dose vitamin D (800IU) or high dose vitamin D (50,000 IU) once a month for 12 months. Outcomes measured were bone density, muscle mass, fall frequency, tests of muscle function and how much calcium women absorbed each day. With treatment, the average measured vitamin D levels were 47 nmol/L in the placebo group, 70nmol/L in the low dose group and 140 nmol/L in the high dose group.

  • There was no effect of taking extra vitamin D on bone density at the hip, lumbar spine or total bone density or on trabecular bone
  • There was no effect of taking extra vitamin D for muscle mass, performance on muscle function tests, number of falls or number of women who had a fall.

The women treated with high dose vitamin D had a small (1%) increase in the amount of calcium they absorbed each day. 7 women in the high dose treatment group were found to have increased calcium levels in their urine, as did one woman in each of the placebo and low dose groups. [High urine calcium predisposes to kidney stone formation].

The authors concluded that although high dose vitamin D may result in a small increase in calcium absorption (1%), this dose not translate into improved bone density or muscle strength in postmenopausal women who do not have osteoporosis.

The findings do not apply to people with known medical conditions that predispose to osteoporosis and fracture, such as people with chronic bowel disease, malabsorption or diabetes mellitus, as women with these conditions were excluded from the study.

In summary this study supports the recommendation of the Institute of Medicine in the US, that a blood vitamin D level of 50nmol/L (20ng/ml) and above is sufficient for healthy muscles and bones in otherwise well postmenopausal women.

[1] Hansen KE, Johnson RE, Chambers KR, et al. Treatment of vitamin D deficiency in postmenopausal women, a randomized clinical trial. JAMA internal medicine. 2015.

What causes Alzheimer’s?

Researchers have done a review of published studies of risk factors for Alzheimer’s Disease (AD) to evaluate what are the modifiable risk factors for AD. The paper published on line in August by the Journal of Neurology Neurosurgery and Psychiatry searched through 16,906 published studies and found 323 which provided information about modifiable risk factors: they identified 93 potential risk factors in this category2.

In research the highest quality evidence is described as “Grade 1” evidence

The modifiable protective factors for which there was Grade 1 evidence were found to be:

  • Ever use of postmenopausal oestrogen therapy
  • current statin use
  • anti-hypertensive medications
  • non-steroidal anti-inflammatory drugs therapy
  • high folate in diet
  • high vitamin E or C in diet
  • coffee consumption

Grade I evidence was found for the following being associated with an increase in the risk of AD:

  • elevated blood homocysteine level
  • depression
  • heavy smoking

A number of other factors were identified as being associated with AD risk such as frailty and obesity, but their associations were more complicated. For example being overweight at midlife was a risk factor, where as having a higher body mass index in later life was protective.
In summary, healthy diet and healthy weight appear to be important for minimizing the risk of AD.

[2]  Xu W, Tan L, Wang HF, et al. Meta-analysis of modifiable risk factors for Alzheimer's disease. J Neurol Neurosurg Psychiatry. 2015.

Information provided might not be relevant to a particular person's circumstances and should always be discussed with that person's own healthcare provider.