Calcium is essential for numerous bodily functions, including bone health, muscle contractions, nerve signaling, and blood clotting. However, a lack of adequate calcium intake can lead to osteoporosis, a condition characterized by weakened bones and an increased risk of fractures. Osteoporosis is particularly prevalent among older adults and individuals with diets low in calcium-rich foods, emphasizing the importance of adequate calcium intake throughout life.
In this blog, we’ll explore how calcium from various sources—animal, plant, and herbal—can help maintain optimal bone health, discuss bioavailability differences, and whether fortified products are a reliable option.
Comparing Calcium Sources: Animal, Plant, and Herbal
Animal-Based Calcium
Animal sources like dairy products (milk, yogurt, cheese) and fish with bones (sardines, salmon) provide calcium with moderate bioavailability, around 30%. Marine sources, such as calcium derived from algae, oyster shells, and fish bones, are becoming increasingly popular for their high absorption rates and additional minerals, such as magnesium, that support bone health.
Research shows that marine-derived calcium promotes bone tissue growth and can act as a sustainable alternative to conventional supplements [1][2].
Plant-Based Calcium
Plant-based foods like kale, broccoli, bok choy, sesame seeds, almonds, and legumes provide calcium, with bioavailability ranging between 50-70%, making them excellent options for non-dairy consumers. The research indicated that some plant sources, such as kale and finger millet, provide calcium levels that can surpass those found in skimmed milk. Specifically, kale was identified as offering five times more bioaccessible calcium per serving compared to skimmed milk. However, spinach was noted for its low bioaccessibility (less than 10%) due to high oxalate content [3].
Other vegetables, including beet greens, also contain oxalates that bind to calcium, reducing absorption. To minimize this effect, cooking or fermenting these foods can lower their oxalate levels, improving calcium availability. Research has demonstrated that cooking methods can significantly reduce oxalate levels in vegetables. For instance, boiling can decrease soluble oxalate content by 30-87%, making it more effective than steaming [4]. Additionally, fermentation processes, such as those used in kimchi preparation, have shown a substantial reduction in oxalate concentrations—up to 72%—thereby increasing the availability of calcium bound to these compounds [5].
Herbal Calcium
Herbs like nettle leaf (Urtica dioica), horsetail (Equisetum arvense), and marine algae offer excellent sources of highly bioavailable calcium along with additional minerals essential for bone health. Nettle is rich in calcium, magnesium, and silica, which support bone density, as well as hair and nails and overall well-being. Studies suggest that nettles can reduce inflammation, help manage blood sugar levels, and support kidney health, making them a versatile addition to a healthy diet [6].
Horsetail, another mineral-rich herb, is particularly high in silica, a compound that plays a crucial role in collagen formation, which strengthens bones and connective tissue. Silica aids in calcium absorption and is known for enhancing skeletal health as well as the connective tissues that keep hair and nails strong. Studies also suggest that silica in horsetail helps regenerate connective tissue and may protect against bone loss associated with aging [7].
Marine algae provide a wealth of health benefits in addition to calcium. Rich in essential trace minerals and anti-inflammatory compounds, marine algae support cardiovascular health and offer antioxidant protection, further enhancing their nutritional profile [8].
Enhancing Calcium Bioavailability
Calcium absorption is influenced by several factors:
Vitamins D and K2:
Vitamin D is necessary for calcium absorption in the gut, while K2 ensures that calcium reaches the bones and avoids depositing in soft tissues like arteries.
Sources of vitamin D include cod liver oil, grass fed butter, and mushrooms exposed to UV light, while fermented foods like natto provide vitamin K2.
Magnesium and Protein:
Both nutrients are essential for calcium metabolism and bone health. Magnesium, in particular, enhances calcium transport across cell membranes. My favorite sources of magnesium include cacao (as a delicious treat) and topical forms like epsom salts (in a bath).
Are Fortified Foods a Good Option?
Calcium-fortified products, such as plant milks, orange juice, and breakfast cereals, can fill dietary gaps, but they are not without drawbacks. These products often contain calcium carbonate or other synthetic forms that require stomach acid for optimal absorption, making them less suitable for individuals with low stomach acidity. Additionally, additives and emulsifiers in fortified foods may disrupt gut health and affect nutrient absorption.
While fortified foods are convenient, they are not a long-term substitute for whole foods or high-quality supplements. Instead, calcium-rich foods like dairy, dark leafy greens, or herbs such as nettles, combined with vitamins D and K2, offer a more holistic and sustainable solution [9].
Recommended Calcium Intake
The daily calcium requirements vary by age, sex, and life stage to ensure optimal bone health and physiological function [10]:
- Infants (0–12 months): 200–260 mg/day
- Children (1–8 years): 700–1,000 mg/day
- Adolescents (9–18 years): 1,300 mg/day (peak growth phase)
- Adults (19–50 years): 1,000 mg/day
- Older Adults:
- Men (51–70 years): 1,000 mg/day
- Women (51–70 years) and all adults 71+ years: 1,200 mg/day
- Pregnant/Breastfeeding Adults: 1,000 mg/day
The upper intake limit (UL) is 2,500 mg/day for adults under 50 and 2,000 mg/day for those over 50, to avoid side effects such as hypercalcemia or kidney stones, or calcification of blood vessels.
Exercise and Calcium Absorption
Regular, weight-bearing exercise is crucial for bone health and osteoporosis prevention. Activities like walking, running, strength training, and even yoga create a natural demand on bones, stimulating bone-forming cells called osteoblasts. This process, known as mechanical loading, enhances bone density and aids in calcium retention by driving calcium into the bone matrix. Exercise not only boosts the absorption of calcium but also helps reduce bone loss, an essential factor for maintaining bone mass as we age.
Conclusion
For a holistic health approach, prioritizing whole-food sources of calcium—such as dairy, leafy greens, nettles, and marine algae—combined with essential nutrients like vitamins D and K2, as well as magnesium and adequate protein, offers the greatest bioavailability. While fortified foods offer convenience, whole foods and carefully selected supplements provide superior absorption and fewer risks associated with overconsumption.
For specific herb/vitamin complex recommendations, I’ve curated my top picks in my herbal dispensary.
References:
- Research progress on applications of calcium derived from marine organisms – PubMed
- The marine-derived, multi-mineral formula, Aquamin, enhances mineralisation of osteoblast cells in vitro – PubMed
- A comparison of the bioaccessible calcium supplies of various plant-based products relative to bovine milk – PubMed
- Effect of different cooking methods on vegetable oxalate content – PubMed
- Effect of Kimchi Fermentation on Oxalate Levels in Silver Beet (Beta vulgaris var. cicla) – PMC
- Nutritional and pharmacological importance of stinging nettle (Urtica dioica L.): A review – PMC
- Inhibition of human in vitro osteoclastogenesis by Equisetum arvense – PMC
- Marine algae: A treasure trove of bioactive anti-inflammatory compounds – ScienceDirect.
- What to Know About Fortified Foods
- Calcium – Consumer
- Davidson, P. L., & Brock, K. E. (2015). The role of calcium and exercise in bone health: Mechanisms and clinical implications. Journal of Bone and Mineral Research, 30(3), 498-507.
- National Institutes of Health. (2022). Calcium and Vitamin D: Important at every age. Retrieved from https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
- Heaney, R. P. (2003). Effects of exercise on bone density and calcium metabolism in humans. American Journal of Clinical Nutrition, 78(3), 493S-497S.
