by C. Leigh Broadhurst, Ph.D.
According to most paleoanthropologists, modern humans developed in Africa between 100,000 and 300,000 years ago, then spread throughout the world.1 During those last 100,000 years, experts believe that human biology didn't evolve significantly. Consequently, they argue, our nutritional needs are dictated more by what our hunter-gatherer ancestors ate than by the foods we eat today.2
Some of our ancestors' foods are noticeably lacking in modern diets--namely, internal organs, bone marrow, skin, tendons, cartilage, bony fish and fibrous plants.3 In contrast to today's average diet, those foods are relatively rich in various nutrients including silicon (Si), an essential trace element researchers think is important to normal bone and connective tissue development. To make matters worse, modern food processing techniques strip our few remaining silicon-containing foods such as grains and rice of nearly all their silicon content--and the health benefits silicon provides.
Silicon is a nonmetallic element that is not found naturally in its pure form because it reacts rapidly with atmospheric oxygen and water. Instead, it is found almost exclusively in silicates, the minerals that constitute geologic rock formations. Silicates are tetrahedral structures of one silicon atom surrounded by four oxygen atoms (see diagram). Although they are the most abundant materials on earth, silicates donít provide bioavailable dietary silicon. When combined with water, silicates convert to orthosilicic acid--the only form of silicon humans can effectively use.4 Orthosilicic acid is one silicon atom bonded to four hydroxides instead of oxygen as in silicates (see diagram). Orthosilicic acid is found naturally in the bloodstream.
When the concentration of orthosilicic acid in water becomes too high, silica forms. Silica is a polymeric silicon-hydroxide-oxide-water complex that can contain up to several trillion silicon atoms. An opal is a silica polymer so large that it is solid. Not all silica polymers are bioavailable, except to the extent that polymers can be broken down to single units of silicon during digestion. Silicates, silica gel, colloidal silica, clays, and most foods and herbal extracts contain silica, not orthosilicic acid, so they are good sources of silicon. In fact, if silica is extracted from herbs such as horsetail into a tincture or tea, the concentrated solution may provide very little absorbable silicon. This is because once the concentration of orthosilicic acid is more than 10 to 100 parts per million in water, the acid's conversion to silica can be prevented only if the solution is chemically stabilized. Thus, to avoid conversion to the substantially less bioavailable silica, large quantities of weak tea might be better than a concentrated extract.
Laboratory experiments on chicks and infant rats demonstrate that silicon is essential for normal skeletal growth.5 Bone is a uniquely flexible material made of apatite crystals (apatite is a calcium-phosphorus mineral) imbedded in a protein matrix containing collagen and glycosaminoglycans. Silicon appears to play a role in the initial stages of bone development when the protein matrix is constructed. It may also increase the rate of bone mineralization and enhance calcium deposition in bone, meaning the bone grows faster and stronger.6
Although a clinical silicon deficiency has not yet been demonstrated in humans, there appear to be situations in which intake and absorption are inadequate. Osteoporosis may be one of them. In a 1993 study conducted by researchers at Centre Hospitalier de Toulon in France, eight women with osteoporosis whose average age was 64 were injected twice weekly for four months with 50 mg of absorbable silicon. According to images taken before and after supplementing, this modest intake significantly increased the density of their thigh bones but did not affect the density of vertebral bone.7 The thigh bone is the largest bone in the body and bears the most weight, so it is an excellent indicator of osteoporosis.
In an animal study conducted in unit 349, Inserm (a French national biomedical research institute) in Paris, female rats were divided into three groups--one had their ovaries removed to simulate menopause, another had a false operation, and the third group was not operated on and served as a control.8 The rats were further divided into groups that either received soluble organic silicon supplementation, the synthetic estrogen hormone estradiol or nothing. Rats whose ovaries were removed experienced an increased rate of bone turnover in their trabecular (fast-growing) bone. Estradiol completely prevented this turnover, and silicon, while not as successful as the hormone, significantly slowed the turnover and increased bone formation rates by 30 percent compared to controls. Bone turnover rate is important--if it shifts out of equilibrium it can result in bone loss and osteoporosis. Many researchers now rely on female patients' bone turnover rate as a marker for osteoporosis. When measuring the rats' total trabecular bone volume, researchers found that untreated rats with ovaries removed had a 50 percent bone loss compared to those with false operations. In the other group of rats whose ovaries were removed, estradiol administration resulted in 8 percent bone loss, while silicon given at 1 mcg per gram body weight resulted in a 42 percent loss.
Although the supplemental silicon did not greatly reduce bone loss, it still makes sense to consider silicon supplementation in conjunction with hormone replacement to help prevent osteoporosis. Silicon supplementation helped to some degree, and there are no reported cases of silicon toxicity. Silicon is also concentrated in the connective tissues of blood vessels, cartilage, hair and skin. Thus, researchers believe it plays an important cross-linking structural role in blood vessel walls as well as in bone.9
Atherosclerosis (blockage and hardening of the arteries by cholesterol plaques and abnormal arterial tissue growth) significantly decreases silicon levels in arterial walls. Silicon levels decrease just prior to plaque development, which may indicate that silicon deficiencies cause inherent weaknesses in blood vessel walls.10,11
Healthy Blood Vessels
Experiments on rabbits at the Experimental Medicine Laboratory, University Pierre et Marie Curie in Paris, showed that silicon supplementation protected against atherosclerotic plaques.12 Thirty-one male rabbits were fed a diet high in cholesterol and peanut oil to produce plaques while 38 were fed the same diet and supplemented with either 7.5-10 mg of silicon every other day intravenously (28 rabbits) or 10 mg to 15 mg per day orally (10 rabbits). Some 77 percent of the 31 rabbits that did not receive silicon developed atherosclerosis, and in 26 percent it was severe. In contrast, only 24 percent of the 38 receiving silicon developed atherosclerosis, and in 16 percent it was severe. Furthermore, of the 28 rabbits receiving silicon intravenously, only 21 percent developed plaques. The arteries of the majority of rabbits given silicon were smooth, shiny, elastic and free from damage--in other words, normal, despite the unhealthy diet. There were no significant differences in the cholesterol or triglyceride levels in rabbits from any group.
Finnish and British studies conducted by researchers at various institutions found that men consumed more than twice the amount of silicon as women--a statistic attributable to the men's beer consumption. Beer drinking aside, normal dietary silicon intakes are 30-50 mg per day, and anywhere from zero to 50 percent is absorbed.13 The causes for such vast differences in absorption have not been determined, but a 50 percent absorption rate is considered good. One study found that silicon was actually in "negative balance" in both men and women, indicating that silicon levels in the body were so low that mineral stores were being released from body tissues to fuel metabolic functions.14
Most animal products except for cartilage, skin and tendons are low in silicon, whereas high-fiber foods such as whole grains, fruits and vegetables are the richest sources of silicon. The refining process, however, removes up to 99 percent of the silicon content in grain (see sidebar above), so supplementing with stabilized orthosilicic acid may be a good alternative.
A study involving 59 calves conducted by Mario Calomme, Ph.D., of the University of Antwerp, Belgium, showed that supplementation with orthosilicic acid was more effective than food in increasing silicon levels in both the bloodstream and in collagen synthesis (a process that requires silicon to cross-link the collagen).15 For 23 weeks, both experimental and control calves were fed a standard milk formula that contained normal dietary levels of silicon. One group of calves was supplemented with 280-380 mcg of orthosilicic acid per gram body weight twice a day. The dosage was increased proportionally as the calves grew. At seven weeks, the calves' daily silicon intake from food was 360 mg and from orthosilicic acid only 17.5 mg. After 23 weeks, however, the silicon levels in the blood of the calves treated with orthosilicic acid was 70 percent higher than controls, indicating a better absorption rate. In a subset of nine calves, the skin collagen content was significantly greater in the calves that received orthosilicic acid compared to calves that did not receive the supplement. This shows that dietary silicon cannot always be absorbed--calves used the supplemental orthosilicic acid even though their diets contained more silicon than did the supplement. According to Calomme, this result also indicates that the calves' ideal silicon requirements were not being supplied by their diets.
Since a calf's growth cycle is much longer than a rodent's, these study results are particularly revealing for humans. Because calves are also better at hydrolyzing silica than rodents, this test better suggests orthosilicic acid's value for humans.
Many factors, including nutrition, hormones, exercise, smoking, alcohol and genetics, play roles in osteoporosis and cardiovascular disease in humans. Preventing these chronic diseases may require a suite of nutrients, including silicon. The list of nutrients and foods recommended for osteoporosis is strikingly similar to that recommended for cardiovascular disease--not surprising, as both bone and arteries are connective tissues.
On the whole, this information strengthens the argument that humans' nutritional requirements are based on paleolithic diets. Both osteoporosis and cardiovascular disease are nutritional diseases of modern Western societies--there is little evidence of hunter-gatherer societies having suffered from either.
NSN C. Leigh Broadhurst, Ph.D., is a geochemist with a lifelong interest in nutrition and preventive medicine. She works as a visiting scientist for a government nutrition research laboratory and heads 22nd Century Nutrition, a nutrition/scientific consulting company in Cloverly, Md. She is also vice president of Herbal Vineyard Inc. in Fulton, Md., headed by James Duke, Ph.D.
1. Stringer, C.B. "Reconstructing recent human evolution." Phil Trans Royal Soc, London B, 337: 217-41, 1992.
2. Broadhurst, C.L., et al. "Rift Valley lake fish and shellfish provided brain-specific nutrition for early Homo." Br J Nutr, in press, 1997.
3. O'Dea, K. "Traditional diet and food preferences of Australian Aboriginal hunter-gatherers." Phil Trans Royal Soc, London B, 334: 233-41, 1991.
4. Carlisle, E.M. "Silicon as a trace nutrient." Sci Total Environ, 73: 95-106, 1988.
5. Nielsen, F.H. "Ultratrace elements of possible importance for human health: An update." In Prasad, A.S., ed., Essential and Toxic Trace Elements in Human Health and Disease: An Update: 355-76. New York: Wiley-Liss, 1993.
6. Carlisle, loc. cit.
7. Eisinger, J. & Clairet, D. "Effects of silicon, fluoride, etidronate and magnesiliconum on bone mineral density: A retrospective study." Magnesiliconum Res, 6: 247-49, 1993.
8. Hott, M., et al. "Short-term effects of organic silicon on trabecular bone in mature ovarectomized rats." Calcified Tissue Internat, 53: 174-79, 1993.
9. Schwarz, K. "Significance and functions of silicon in warm-blooded animals." In Bendz, G. & Lindquist, I. eds., Biochemistry of Silicon and Related Problems: 207-30. New York: Plenum Press, 1978.
10. Nielsen, loc. cit.
11. Schwarz, loc. cit.
12. Loeper, J., et al. "The antiatheromatous action of silicon." Atherosclerosis, 33: 397-408, 1979.
13. Pennington, J.A.T. "Silicon in foods and diets." Food Additives Contamin, 8: 97-118, 1991.
15. Calomme, M.R. & Vanden Berghe, D.A. "Supplementation of calves with stabilized orthosilicic acid. Effect on the Silicon, Ca, Mg, and P concentrations in serum and the collagen concentration in skin and cartilage." Biol Trace Elem Res, 56: 153-65. 1997
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