A listener on a radio program shared that her doctor recommended she separate vitamin D from calcium. It is possible she was confused, but a piece of data was missing – regarding which supplement she takes and what else it contains. On one hand, vitamin D actually helps with calcium absorption. On the other hand – if the supplement itself contains calcium, then it is advisable to separate. A calcium overload all at once reduces absorption to a certain extent, and it is a shame to lose out. Let us clarify the matter:
Vitamin D is essential for the absorption of calcium from food. Without vitamin D, the body finds it very difficult to transfer calcium from the intestine to the blood. One of the central roles of vitamin D is to activate special proteins in the intestine that allow calcium to be absorbed more efficiently. This is precisely the reason why a significant deficiency in vitamin D can lead to a decrease in bone density, even if enough calcium is consumed in the diet.
A study published in the Journal of Bone and Mineral Research showed that low levels of vitamin D are linked to a decrease in calcium absorption and an increase in the risk of fractures in older age.
How much vitamin D is needed?
Vitamin D is sometimes called the "sunshine vitamin," but in practice, for quite a few people in sunny Israel, its levels are actually low. The reason is that although there is plenty of sun here, most of the day we are inside buildings, in the car, or in the office, using sunscreens, and sometimes also avoiding direct exposure to the sun due to the heat or fear of skin damage.
Unlike most vitamins, vitamin D hardly comes from food in a significant amount. Its main sources are:
Fatty fish such as salmon, mackerel, and sardines
Egg yolk
Liver
Dairy products or fortified beverages
And sometimes mushrooms exposed to UV radiation
But even a good diet is usually not enough to reach high levels in the blood.
So it is important to mention and remember – the body manufactures most of its vitamin D by itself with the help of sun exposure: When UVB rays hit the skin, the body begins a natural production process of the vitamin.
How much time do you need to be in the sun? It depends on the season, age, skin color, amount of clothing, and time of day.
In the summer in Israel, sometimes even 10–15 minutes of exposure to the hands and face at the appropriate hours can be enough for some people, but in older adults, the production of the vitamin in the skin decreases significantly with age.
But, despite the Israeli climate, studies in Israel found that the rate of vitamin D deficiency is very high. According to data published in the Israeli Medical Association Journal and in studies by the health funds, in some populations in Israel, more than half of the subjects were found with levels lower than the recommendations, especially older adults, women, people who rarely go out into the sun, and people with excess weight.
Today, the recommendations for supplements vary by age and medical condition, but most guidelines speak of:
About 600 international units (IU) a day for young adults
About 800 IU over the age of 70, in practice, due to common deficiency, many doctors recommend higher doses according to blood tests
Sometimes 1000–2000 IU a day, and in cases of significant deficiency even more, under medical supervision.
It is also important to remember that vitamin D is a fat-soluble vitamin, and therefore there is no point in taking huge doses "just to be safe." An extreme excess over time can be harmful and cause a dangerous rise in calcium levels in the blood.
Why separate calcium from vitamin D?
In most cases, it is not a matter of separating vitamin D from calcium, but rather separating large calcium doses. The reason is that the body is incapable of efficiently absorbing a huge amount of calcium all at once. When taking, for example, 1000–1200 mg of calcium together, part of the amount is simply not absorbed.
This is the reason why it is sometimes recommended to divide the amount: 500–600 mg in the morning, and another dose in the evening. This is especially true for supplements, and less relevant to calcium that comes from food throughout the day.
The type of calcium also matters: Not all calcium supplements are identical: Calcium carbonate, for example, is absorbed better when taken with food, because it needs stomach acidity. In contrast, calcium citrate is absorbed even without a meal, and is sometimes more suitable for older people or for those taking medications to reduce stomach acidity. A study published in Osteoporosis International found that calcium citrate is absorbed better among older adults with reduced stomach acidity.
Calcium and other supplements – when do you need to separate?
There are cases where it is actually recommended to distance calcium from medications or other supplements. For example: Iron, zinc, thyroid medications, and certain antibiotics. The reason is that calcium might bind to them in the intestine and reduce their absorption. Therefore, the feeling is sometimes mistakenly created that "it is forbidden to take calcium with vitamin D," even though the problem is completely related to another medication being taken concurrently.
In conclusion, it is important to emphasize – do you have to take calcium supplements? Really not always. Many people can reach a fine amount of calcium through foods like yogurt, cheeses, tahini, almonds, sardines with the bones, and certain green vegetables.
Sun exposure also assists in the production of vitamin D in the body, although in Israel quite a bit of deficiency is still seen, especially among older adults, people who stay home a lot, or those who are very strict about sun protection.
The bottom line – vitamin D does not interfere with calcium absorption, but rather the opposite – it is essential for it. The confusion usually stems from recommendations to divide large calcium doses, or from the need to distance calcium from other medications. That is: Vitamin D and calcium can definitely be taken together, but it is not always advisable to take a very large amount of calcium all at once, and in cases of certain medications, it is important to check specific instructions.