Vitamin D & Mineral = Calcium
Vitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). Vitamin D obtained from sun exposure, food, and supplements, is biologically inert and must undergo two hydroxylation reactions to be activated in the body. Calcitriol (1,25-Dihydroxycholecalciferol) is the active form of vitamin D found in the body. The term vitamin D also refers to these metabolites and other analogues of these substances.
Calcitriol plays an important role in the maintenance of several organ systems. However, its major role is to increase the flow of calcium into the bloodstream, by promoting absorption of calcium and phosphorus from food in the intestines, and reabsorption of calcium in the kidneys; enabling normal mineralization of bone and preventing hypocalcemic tetany. It is also necessary for bone growth and bone remodeling by osteoblasts and osteoclasts.
Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Deficiency can arise from inadequate intake coupled with inadequate sunlight exposure; disorders that limit its absorption; conditions that impair conversion of vitamin D into active metabolites, such as liver or kidney disorders; or, rarely, by a number of hereditary disorders. Vitamin D deficiency results in impaired bone mineralization and leads to bone softening diseases, rickets in children and osteomalacia in adults, and possibly contributes to osteoporosis.
Vitamin D plays a number of other roles in human health including inhibition of calcitonin release from the thyroid gland. Calcitonin acts directly on osteoclasts, resulting in inhibition of bone resorption and cartilage degradation. Vitamin D can also inhibit parathyroid hormone secretion from the parathyroid gland, modulate neuromuscular and immune function and reduce inflammation.
Sub-optimal vitamin D levels have been linked with fibromyalgia, rheumatoid arthritis, multiple sclerosis, upper respiratory tract infections, premenstrual syndrome, polycystic ovary disease, psoriasis, muscle weakness, lower back pain, diabetes, high blood pressure, and cancer.* Bone pain is another symptom that sometimes clears up upon vitamin D supplementation. One study reported that the only side effect of vitamin D supplements was “improved mood,” *indicating that perhaps vitamin D is linked to depression. This makes sense given that many people often become depressed when they are deprived of sunshine for long periods.
There are two types of vitamin D:
- Vitamin D3 – cholecalciferol; is derived from animals (usually from sheep’s wool or fish oil).
- Vitamin D2 – ergocalciferol; is vegan and usually obtained from yeast.
Most Americans get vitamin D through sunshine, fortified milk, and fortified margarine. The only significant, natural sources of vitamin D in foods are fatty fish (e.g. cod liver oil,mackerel, salmon, sardines), eggs (if chickens have been fed vitamin D), and possibly some wild mushrooms. The vegan diet contains little, if any, vitamin D without fortified foods or supplements.
Vitamin D in Fortified Foods
- The Daily Value for vitamin D is 10 mcg (400 IU). Therefore, if a food label says it has 25% of the daily value, it means it has 2.5 mcg (100 IU) per serving.
- Vitamin D fortified soy, almond, or rice milk normally has 2-3 mcg (80-120 IU) per cup.
Calcium is the chemical element with the symbol Ca and atomic number 20.
Calcium is a soft gray alkaline earth metal, and is the fifth most abundant element by mass in the Earth’s crust. Calcium is also the fifth most abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.
Calcium is essential for living organisms, particularly in cell physiology, where movement of the calcium ion Ca2+ into and out of the cytoplasm functions as a signal for many cellular processes. As a major material used in mineralization of bones and shells, calcium is the most abundant metal by mass in many animals.
Calcium is important for bones because it is a major component of bones, which are constantly being broken down and built back up. Vitamin D regulates calcium absorption and excretion, especially when calcium intake is low.
Calcium is a component of bones, but is more immediately needed in the blood to keep muscles, such as the heart, contracting efficiently. The body preserves blood calcium levels at the expense of bone calcium.
When calcium levels in the blood drop, parathyroid hormone (PTH) is released. PTH causes calcium to be released from the bones, thus raising the low calcium levels in the blood. Osteoporosis may result from chronically high levels of PTH.
Vitamin D is the building block of the hormone calcitriol which works synergistically with PTH. Vitamin D is modified by the liver to become 25-hydroxyvitamin D (also known as 25(OH)D). 25(0H)D is then modified in the kidneys to become calcitriol. This conversion is somewhat regulated by PTH levels.
Calcitriol increases absorption of calcium and phosphorus (another major component of bones) from the intestines and decreases their excretion in the urine. In so doing, calcium levels in the blood rise and PTH levels drop.
Calcitriol has many other functions. How the body regulates the processes of conversion of vitamin D into calcitriol and the resulting net increase or decrease of bone calcium are not fully known.
- The calcium in kale, broccoli, collard greens, and soymilk is all absorbed relatively well.
- The calcium in spinach, Swiss chard, and beet greens is not well absorbed, due to their high content of oxalates, which bind calcium.
- Calcium supplements can inhibit iron absorption if eaten at the same time.
- In addition to the calcium in the leafy greens listed, leafy greens also contain vitamin K which is good for bones. (Vitamin K info later!
|veg baked bean
*Schwalfenberg G. Not enough vitamin D: health consequences for Canadians. Can Fam Physician. 2007 May;53(5):841-54.
bRead the label for calcium amounts
T – tablespoon