What is Strontium?
Strontium (Sr) is a naturally occurring alkaline earth metal, chemically similar to calcium (Ca). This similarity means the body processes and stores strontium in a comparable way to calcium, with approximately 99% of the body's strontium concentrated in the bones and teeth. The stable form of strontium, not to be confused with the radioactive isotope Sr-90 from nuclear fallout, is a normal component of the human diet. While strontium is found widely, its concentration in food depends on environmental factors, primarily the mineral content of the soil and water used for farming. A normal daily intake is relatively small, estimated at around 0.5 to 1.5 mg, which is sourced from various dietary items.
Food Groups Containing Strontium
Numerous food categories contribute to the daily intake of stable strontium. Due to varying environmental factors, the exact amount can differ, but certain food groups are consistently identified as reliable sources.
Seafood
Seafood is widely recognized as one of the richest dietary sources of strontium. Marine organisms, particularly those that filter water, tend to concentrate the mineral. Excellent options include:
- Shellfish: Oysters and scallops are particularly high in strontium, reflecting their filter-feeding nature.
- Fish: Both fatty and lean fish species contain strontium absorbed from their aquatic environment.
Vegetables and Legumes
The strontium content in plant-based foods is highly dependent on the soil they are grown in. Generally, leafy and root vegetables are better sources than fruits.
- Leafy Greens: Vegetables such as spinach, lettuce, and cabbage can contain notable amounts of strontium.
- Root Vegetables: Carrots, potatoes, parsnips, and celery absorb minerals directly from the soil, making them good sources.
- Legumes: Beans, in particular, are a significant dietary source of strontium.
Grains and Nuts
Whole grains and nuts are also key contributors to dietary strontium, particularly unrefined varieties. The outer layers and bran of grains often contain higher concentrations.
- Whole Grains: Wheat, barley, and wheat bran are identified as good sources.
- Nuts: Brazil nuts are frequently cited as a good source of this trace element.
Dairy and Animal Products
Strontium is transferred through the food chain, meaning animal products also contain the mineral, reflecting their dietary intake. Certain dairy products, in particular, are good sources.
- Dairy Products: Whole milk, cream, and hard cheeses contain strontium. Some studies suggest lower-fat dairy like skim milk may contain higher concentrations relative to their fat content.
- Other Animal Products: Meat, poultry, and eggs also contain small amounts of strontium.
Factors Influencing Strontium Levels
Several factors determine the strontium levels in food and drinking water:
- Soil and Water Content: The primary determinant is the local geology. Areas with strontium-rich rock and soil lead to higher concentrations in both water and agricultural products grown there.
- Water Source: Groundwater typically contains higher levels of strontium than surface water. This is because minerals leach from rocks and soil over time, concentrating in underground water sources.
- Food Processing: Refined grains, for example, lose a significant amount of their mineral content, including strontium, as the bran is removed.
- Cooking Methods: Using water with higher strontium concentrations to prepare foods can increase their final strontium content. One study showed that lentils, broccoli, and spaghetti absorbed strontium from the cooking water.
Comparison: Strontium vs. Calcium
Given their chemical similarities and interaction in the body, understanding the differences between strontium and calcium is crucial. Both are alkaline earth metals, but their biological handling is not identical.
| Feature | Strontium (Sr) | Calcium (Ca) |
|---|---|---|
| Abundance | A trace element in the human body, but 15th most abundant element in the Earth's crust. | The most abundant mineral in the human body, critical for bone structure and other functions. |
| Primary Dietary Source | Vegetables, whole grains, seafood, and dairy. Varies heavily with geography. | Primarily dairy products, leafy greens, fortified foods, and supplements. |
| Absorption Rate | Generally less efficiently absorbed in the intestines than calcium. | Efficiently absorbed, though absorption can be affected by factors like vitamin D status. |
| Homeostasis | Not under homeostatic control in the body in the same way calcium is. | Tightly regulated to maintain proper blood levels, controlled by hormones like PTH and calcitriol. |
| Bone Action | Incorporated into bone, particularly on surfaces of new bone. Can be beneficial for bone density at low doses. | The fundamental building block of bone mineral; high levels are essential for bone strength. |
| Excess Risk | Can weaken bones if too much replaces calcium, especially with low calcium intake. | High intake from supplements can pose health risks, but is less likely to directly weaken bone. |
What is the Role of Strontium in the Body?
The body's main function for stable strontium relates to bone tissue. Because of its chemical similarity to calcium, strontium is incorporated into the bone mineral matrix, especially in newly forming bone. Research indicates that appropriate levels of strontium can play a positive role in bone health by:
- Promoting bone formation: It can increase the activity of osteoblasts, the cells responsible for building new bone tissue.
- Inhibiting bone resorption: Strontium can also decrease the activity of osteoclasts, the cells that break down old bone.
- Strengthening tooth enamel: Preliminary evidence suggests that strontium may also help protect against dental cavities by strengthening tooth enamel.
While prescription strontium ranelate has been used to treat osteoporosis, it is not available in the U.S. and has been associated with serious side effects, leading to restricted use in Europe. Normal dietary intake of stable strontium does not present these same risks, but it is important to maintain a balanced diet with adequate calcium and vitamin D to support bone health.
Conclusion
Strontium is a trace mineral that is naturally present in a variety of foods and water sources. Key dietary sources include seafood, whole grains, dairy products, and certain vegetables, though the mineral's concentration can vary significantly based on environmental and agricultural factors. Due to its chemical resemblance to calcium, strontium is primarily stored in bones, where it influences the balance between bone formation and resorption. While a normal dietary intake of stable strontium is generally considered safe and may offer minor benefits for bone health, it is a trace element, and excessive consumption, particularly in supplement form, can be detrimental. A balanced diet with adequate calcium and vitamin D remains the most effective strategy for robust bone health. Further research is needed to fully understand the long-term effects of dietary strontium intake and its optimal levels for human health.
Outbound Link
For more detailed information on strontium and other minerals, consult the National Institutes of Health (NIH) website.
