Boron Supplementation for Low Bone Density and Osteoarthritis
Boron Supplementation for Low Bone Density and Osteoarthritis
By Sharon L. Kolasinski, MD, FACP, FACR
Although the benefits of calcium supplementation are well known and accepted by physicians and the public alike, a variety of additives to calcium supplements have appeared in the marketplace that have less clear indications for general use. In search of better bone health, consumers must choose among supplements with added vitamin D, magnesium, glucosamine, and other ingredients. The consumer is now faced with yet another choice: Should she buy calcium supplements with or without boron?
In nature, boron is found in fruits, vegetables, legumes, and nuts. Boron also presents as a naturally occurring trace element in human bone. Bone matrix is composed of 90% type I collagen fibers and 10% noncollagenous proteins. The degree of mineralization of the bone depends on its location: Up to 90% of cortical bone is calcified, whereas only about 25% of spongy or trabecular bone is calcified. Trace elements include boron, as well as zinc, manganese, magnesium, and aluminum. These elements are present in both the mineralized and non-mineralized portions of bone, and their role in normal bone functioning, as well as in disease states, is not completely understood. Boron may have numerous and interdependent effects on hormone levels and bone metabolism.
Pharmacokinetics
Boron is readily and completely absorbed on oral administration.1 It is rapidly distributed throughout the body water and the concentration in blood and soft tissue is the same, whereas the relative concentration in bone, nails, and hair is relatively increased. One widely quoted observation is that an increase in oral boron intake does not lead to a similar rise in plasma boron concentration.2 Rather, a marked increase in urinary boron will accompany an increase in oral intake, suggesting the presence of a renal homeostatic mechanism.
Unlike many other minerals, boron is water-soluble. Boron is not metabolized and over 90% is excreted unchanged in the urine with a half-life of 21 hours. Because there are no useful serum markers of biological activity of boron, urine levels have been used as an outcome measure of boron supplementation. However, two findings make interpretation of urinary excretion data difficult. First, healthy volunteers may vary 10-fold in the amount of daily boron excretion. In addition, it is unknown whether the amount of boron excreted correlates with physiologic effects.3
Metabolism
Boron metabolism is intertwined with that of other minerals, including calcium, copper, magnesium, and phosphorus. The literature in animals, as well as in humans, addressing the role of boron in bone metabolism is both complex and confusing as a result. Animal data have suggested that phosphorus and magnesium levels in laboratory animals may be adversely affected if boron deficiency occurs. Calcium levels have been shown to vary with boron levels when potassium is manipulated in the diet.4
Physiology
The physiologic effect of boron is unknown. Characteristics of a boron deficiency state in humans have not been described. In blood, boron combines with hydroxyl groups and is known to form complexes with organic compounds containing hydroxyl groups in favorable positions. Identified interactions include those with serine proteases, nicotinamide adenine dinucleotide, pyridoxine, riboflavin, glycoproteins, and polysaccharides.5
Non-Medical Uses
Urban dwellers may be familiar with boron as the active ingredient in a number of roach-killing products. In fact, the Australian government issued a regulation that cited boron as a poison, substantially reducing sales of boron supplements for a time.6
Bone Mineral Density
Many clinical trials manipulate multiple mineral levels within a single study. Some authors suggest that this type of experimental design more closely models conditions of nutritional stress.4 However, it is unclear how the manipulated levels of minerals relate to variations in human diets or to disease states and their potential treatments.
In healthy subjects, boron levels may vary with age, nutrition, hormonal status, or other factors. Work by one group suggested an important relationship between boron levels and excretion of calcium and magnesium.7 Eleven postmenopausal women with an average age of 61 years lived in a metabolic unit for 167 days. They were fed a low-boron diet at baseline and were supplemented with 3 mg of boron daily for 24 days. They appeared to have a dramatic reduction in calcium and magnesium urinary excretion. The authors suggested that boron might have an important role in the treatment of postmenopausal osteoporosis since boron supplementation might reduce loss of calcium in the urine.
A more complete reporting of data on this original group of 11 women was published a decade later.2 It was noted that the effect of boron on calcium excretion, and other effects, was dependent upon magnesium. In fact, urinary excretion of calcium was increased in the presence of boron supplementation when magnesium supplementation was given as well. Boron supplementation led to narrowing of the QRS complex in the absence of magnesium supplementation and was associated with an increase in systolic and diastolic blood pressure, regardless of magnesium supplementation. Neither effect took participants out of the normal range.
A study by a different group of investigators failed to demonstrate a correlation between boron supplementation and reduced mineral excretion.8 In this study, healthy sedentary and athletic college women received 3 mg/d of boron and were followed for 10 months. Although the small size of the study (26 subjects) limits its power, the authors could not demonstrate any significant correlation between boron and excretion of calcium, phosphorus, or magnesium. Serum levels of phosphorus were lower and serum levels of magnesium were higher in those supplemented with boron, but they also were influenced by exercise. This widely cited study has added to the appreciation that the role of boron in the body is likely to be related to numerous other factors.
Hormones, Osteoporosis, and Menopause
In addition to the suggestion that boron levels may vary with hormonal status, boron itself may alter hormone production. Neilsen and colleagues showed in their early work that boron supplementation could result in increased 17 b-estradiol and testosterone levels in postmenopausal women.7 In a study of seven healthy male volunteers with an average age of 26 years, boron supplementation of 10 mg daily for four weeks also was associated with a significant increase in plasma estradiol levels.2 However, in these young men, there was no significant change in testosterone levels. The authors suggested that boron may be of cardiovascular benefit in young men, but no data were supplied to support this contention. Whether boron may exert effects on bone mineral density as a result of effects on estrogen levels has not yet been explored. No studies have yet followed actual bone mineral density measurements to assess a direct effect of boron supplementation on clinically significant osteoporosis.
A corollary of the supposition that boron has important interactions with estrogen levels is the suggestion that it be used to treat perimenopausal symptoms. One group followed electroencephalograms (EEG) and tests of cognitive, spatial, and psychomotor functioning in subjects on boron. Several experiments were performed and each involved a small number of participants, including postmenopausal women who varied with respect to whether they took hormone replacement therapy. EEG findings were consistent with what had been found in animals: Low boron intake (< 0.3 mg/d) was associated with EEG patterns suggestive of drowsiness and low mental alertness. Low boron intake consistently was associated with a reduction in memory and attention on psychological testing.9
An additional trial specifically looked at boron’s effects of the functioning of perimenopausal women. Forty-six women participated in this double-blind, crossover trial in which all women took boron supplementation of 3 mg/d as sodium tetraborate at some point in the trial. Subjects completed daily symptom checklists. Boron supplementation was associated with an increase in vasomotor symptoms, sleep disturbance, and total symptoms (including depression, anxiety, and somatic symptoms).10
Osteoarthritis
One study has shown that boron levels, along with those of lead and zinc, were reduced in patients with osteoarthritis of the hip when those patients went for hip replacement.11 Surgical specimens of femoral heads revealed an overall reduction in mineralization, which researchers speculated reflected increased bone turnover that is part of the osteoarthritic disease process. Interestingly, the level of demineralization in the osteoarthritis patients was greater than in a group of patients who were undergoing hip replacement due to fractures of the femoral neck.
Some have speculated that boron might be a useful supplement for patients with osteoarthritis.12 Although boron may be reduced in certain disease states, it is less clear that boron supplementation will alter the risk or severity of arthritis. The only study to address the question found no significant difference between a group of osteoarthritis patients given 6 mg daily of boron as sodium tetraborate for eight weeks and a group given placebo. Although the study was double-blind and placebo-controlled, only 20 patients were enrolled and a quarter dropped out due to lack of efficacy.13 Outcome measures used were subjective and did not include standard benchmarks of improvement used in osteoarthritis research.
Adverse Effects
Boron toxicity results in behavioral depression, hypotonicity, ataxia, poor motor control, impaired operant learning of avoidance tasks, and drowsiness.9 In addition, boron toxicity adversely affects fertility.14 More severe intoxication may result in restlessness, tremor, confusion, and seizures.
Formulation and Dosage
Boron generally is not available as an individual supplement, but is an ingredient in some multivitamins and calcium preparations. In the combination products, the dosage of boron generally is 1 or 2 mg per tablet.
The minimum daily requirement for boron has not been established.
Conclusion
The exact physiologic role of boron is not clear. It may affect bone metabolism, especially in conjunction with other minerals and vitamin D, with which it appears to have complex, interdependent relationships. It may modulate sex hormone production in men and women, alter cognitive function, and provide analgesia for arthritis sufferers, but data are preliminary at best in all of these areas of clinical application. Toxicity includes adverse central nervous system and reproductive effects.
Recommendation
Boron supplementation cannot be recommended on the basis of current research. Its basic role in metabolism of bone and the reproductive system remains unclear, as do its possible preventive or therapeutic uses. Considerably more research needs to be done to establish its role in health and disease. v
Dr. Kolasinski is Assistant Professor of Medicine; Director, Rheumatology Fellowship Program; and Chief of Clinical Service, Division of Rheumatology at the University of Pennsylvania School of Medicine in Philadelphia.
References
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11. Helliwell TR, et al. Elemental analysis of femoral bone from patients with fractured neck of femur or osteoarthrosis. Bone 1996;18:151-157.
12. Gaby AR. Natural treatments for osteoarthritis. Altern Med Rev 1999;4:330-341.
13. Travers RL, et al. Boron and arthritis: The results of a double-blind pilot study. J Nutr Med 1990;1:127-132.
14. Benderdour M, et al. In vivo and in vitro effects of boron and boronated compounds. J Trace Elem Med Biol 1998;12:2-7.
Kolasinski S. Boron supplementation for low bone density and osteoarthritis. Altern Med Alert 2002;5:18-21.Subscribe Now for Access
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