Significance of Dietary Calcium and Vitamin D for Osteoporosis in Women
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| Human Internal Body Structure |
The conclusions summarized below are based on the latest available data.
- Is there a Rationale for Supplementing Postmenopausal Women with Calcium and Vitamin D?
To answer this question, it is necessary to define the minimum thresholds of vitamin D and calcium consumption below which bone health is compromised. Ideally, these rates should depend on a relationship between food intake and a quantified bone health index. For vitamin D, a plausible threshold can be established as several studies have demonstrated a link between low blood levels of 25-hydroxyvitamin D (25 [OH] D) and increased secretion of parathyroid hormone. The latter causes bone loss in the elderly because of an increase in bone resorption. In the literature, it is estimated that the blood level of 25 (OH) D required to maintain normal PTH levels should be between 30 and 100 nmol / l. In a study of 8532 postmenopausal and osteoporotic women, 79.6% had vitamin D insufficiency if a blood threshold of 25 (OH) D was set at 80 nmol / l, versus 32.1% with a threshold of set at 50 nmol / l. The experts agreed that the threshold of 80 nmol / l may have been overestimated, 50 nmol / l being more reasonable and acceptable.
The question of an acceptable threshold for calcium intake is much less clear and the recommendations vary between 400 and 1500 mg / d. There is no evidence that countries with the lowest consumption are at higher risk of osteoporotic fracture. In addition, there are few long-term studies that take into account the slow adaptation to changes in food intake. For these reasons, it has been agreed that there is insufficient evidence to recommend routine calcium supplementation for women who do not have an increased risk of developing osteoporosis.
In contrast, the majority of studies that evaluated the effects of calcium and vitamin D supplementation in postmenopausal women demonstrated a decreased risk of fracture when adherence to treatment was sufficient (75-80%).
Experts have reached the following consensus: calcium and vitamin D supplementation should be recommended for women with high risk of osteoporosis, osteopenic women, and those with osteoporosis. For vitamin D, the dosage should be sufficient to ensure that blood levels of 25 (OH) D reach the threshold of 50 nmol / l.
- Is it Justified to use Different Doses of Calcium and Vitamin D depending on the Age of the Subject?
The need for calcium and vitamin D supplementation may be increased in the elderly for several reasons. In general, the consumption of calcium and vitamin D decreases in the elderly, as does the efficiency of the endogenous production of calcitriol. Intestinal absorption and renal tubular renal reabsorption decrease with age, as well as the ability to adapt to a diet low in calcium.Age is a very important factor of fracture risk. Having agreed that calcium and vitamin D supplementation should be aimed at individuals at high risk of fracture, elderly people, especially those over 65, are particularly affected by this supplementation. It was therefore agreed that for people over 65, supplementation should be recommended without the need for a prior assessment of their status. However, younger women with low intake and / or high risk of fracture should also receive adequate supplementation after appropriate examinations. Calcium intakes can be checked very simply and at a lower cost, but this is not the case for 25 (OH) D. It has been agreed, from a pharmacoeconomic point of view, that vitamin D supplementation, in addition to calcium, may be warranted in women under 65 years of age with a proven calcium intake deficit; indeed, the combination of calcium and vitamin D could reduce bone remodeling. In terms of dose, it is likely that there is a risk gradient that corresponds to a suitable dose gradient. As a result, higher risk individuals may benefit from higher doses than those with lower risk.
Many studies have shown that the duration and compliance of supplements are often unsatisfactory and that lack of compliance reduces or eliminates efficacy. It is necessary to remember this when defining a dosage, both in terms of efficacy and pharmacoeconomic terms. It has been decided that to be effective, vitamin D supplementation must be sufficient to reach the acceptable threshold of 25 (OH) D. Studies evaluating the anti-fracture efficacy of different doses of vitamin D have demonstrated that 400 IU / d were not sufficient to act effectively on the fracture rate and that it would be better to combine vitamin D and calcium. Oral doses greater than 700 IU / d or 100,000 IU quarterly have an anti-fracture effect, while an intramuscular dose of 300,000 IU annually has variable efficacy. Thus, supplementation is more effective for osteoporotic patients when administered orally, either daily or quarterly. If taken daily, the minimum dose should be between 700 and 800 IU / d.
- Add Calcium to Vitamin D Supplementation, or Add Vitamin D to Calcium Supplementation, Is it Interesting?
In the current state of our knowledge, it seems that while calcium plays a role in the prevention of fractures when it is associated with vitamin D, this effect can not be attributed to calcium alone. A meta-analysis of data from randomized clinical trials found that vitamin D supplementation alone was insufficient to reduce the relative risk of hip fracture in postmenopausal women. However, supplementation with a combination of calcium and vitamin D reduced the risk of hip fracture by 28% and reduced the risk of non-vertebral fracture by 23%, compared to vitamin D alone. Two recent studies seem to contradict this theory (the RECORD study and the Women's Health Initiative [WHI]), but it is important to note that no study has targeted subjects at high risk of fracture. The RECORD study did not evaluate blood levels of vitamin D or the parathyroid response, so it is not known if the subjects had vitamin D deficiency. In addition, the number of fractures in this study was reduced and adherence was low, suggesting that the power calculation of the study was not good. The clinical study of WHI was conducted in healthy postmenopausal women with mean calcium intake greater than 1000 mg / day and 80% of these women were under 70 years of age. The vitamin D level at baseline was only known for 1% of subjects and the vitamin D dosage was 400 IU, a level that other studies deemed insufficient to have an effect on the fracture rate. In addition, adherence was low, estimated at less than 60%. However, an analysis performed only on observing subjects demonstrated a significant reduction in the risk of hip fracture.In conclusion, in order to reduce the risk of fracture, supplementation should be administered at doses adjusted to baseline levels of approximately 800 IU vitamin D and 1000-1200 mg calcium per day. However, this supplementation should target those at higher risk of fracture than the population included in these two studies.
- Should Special Precautions be Taken in Case of Calcium and / or Vitamin D Supplementation in Postmenopausal Women?
There are no warnings or precautions for the use of vitamin D and calcium in the case of postmenopausal women. This supplementation should be prescribed with caution in patients with renal impairment. High dose supplementation creates a risk of hypercalcemia with renal dysfunction. Special attention is also needed in patients with cardiovascular pathology, as the effect of digitalis may be potentiated by supplementation with vitamin D and calcium. The use of calcium supplementation may cause mild gastrointestinal dysfunction, such as constipation, flatulence, nausea, stomach pain and diarrhea.
- Should Calcium and / or Vitamin D be Combined with Anti-osteoporosis Treatments?
The vast majority of efficacy studies of anti-osteoporosis treatments are based on the combination of these treatments with calcium and vitamin D supplementation. It has been demonstrated in humans as well as in animals that vitamin deficiency D reduces the effectiveness of some osteoporosis treatments. In addition, preclinical studies have shown that the effectiveness of bisphosphonates is reduced when animals are dieted in a low vitamin D diet. Therefore, it is concluded that anti-osteoporosis treatments should be prescribed in combination with calcium supplementation. vitamin D. The combination of anti-osteoporosis treatments with calcium alone or vitamin D alone has been studied very little.
Conclusion
Supplementation with calcium and vitamin D can be justified, both in terms of efficacy and health economics, in women at increased risk of osteoporotic fracture, including those who do not have a fracture yet. Are considered at increased risk of fracture, women over 65 years or younger women if they are osteopenic and / or have insufficient calcium and / or vitamin D intake. In addition, vitamin-calcium supplementation is recommended for women receiving other osteoporosis treatments.
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