Vitamin D Supplementation: How to Avoid Overdoing It!
Vitamin D Supplementation: How to Avoid Overdoing It!
What is it?
Vitamin D is a fat-soluble vitamin that functions as a hormone precursor. Known as cholecalciferol, it is found in oily fish such as herring as well as cheese, egg yolk, and beef liver.
The main way to get the “sunshine vitamin” is through exposure to sunlight or other sources of ultraviolet light. Vitamin D is inactive until it is hydroxylated or activated first by the liver and then by the kidneys. The active form of vitamin D is 1,25 dihydroxy vitamin D.
The vitamin D most commonly measured on a blood test is the 25 dihydroxy vitamin D – the inactive form. The active form is not commonly measured because it has a short half-life.
Most supplemental vitamin D is in the D3 form. However, doctors have been known to prescribe D2 to patients with a deficiency. It is important to know that the D3 form is 3-9 times more potent than the D2 form (Gaby, 2017).
What does it do?
Vitamin D performs many functions:
It enhances the intestinal absorption of calcium and phosphorus
It promotes bone mineralization,
It modulates the immune system
It plays a role in neurotransmitter function
It is a powerful steroid hormone
Vitamin D also acts as a negative acute phase reactant meaning that when someone is sick or has high levels of inflammation, their vitamin D will drop. Many people assume that low vitamin D is the cause of illness or adverse outcomes when in reality it is most likely the result of inflammation (Mangin, Sinha & Fincher, 2014).
What is an ideal range for vitamin D?
Welcome to the great controversy over the so-called optimal range for vitamin D! Over the years, the recommendations for how much to take have been skyrocketing.
Currently, the Vitamin D Council defines “sufficient” as between 40-80. The Endocrine Society defines “insufficiency” as between 20-29. The Institute of Medicine defines “sufficient” as 20 or above.
The Institute of Medicine (IOM), also known as the National Academy of Science, is the country’s leading authority regarding medical research. When they make recommendations, they are trying to avoid long-term unanticipated consequences to the general public. Therefore, they tend to be cautious.
In 2010, the IOM issued a report stating that most vitamin D recommendations “have not been set using rigorous standards” (Mangin, Sinha & Fincha, 2014). Furthermore, vitamin D levels are based on average values from a population that has been supplementing for decades. This means that today’s healthy population may have higher vitamin D levels than the healthy population from 50 years ago.
Interestingly enough, low vitamin D is also found in both sick individuals and healthy individuals with adequate exposure to sunlight (Mangin, Sinha & Fincher, 2014).
It is difficult (if not impossible) to find reliable clinical trials in which aggressive supplementation with vitamin D was shown to improve or reserve a health condition. There is, however, clear evidence to support raising vitamin D levels in patients with a true deficiency for almost all health conditions.
Many Americans, especially at either end of the age spectrum, are vitamin D deficient. For example, breast milk is low in vitamin D compared to fortified milk and formula. For this reason, the American Academy of Pediatrics recommends that all breastfed infants receive 400 IU daily of supplemental vitamin D.
Lastly, it is important to know how a given lab measures vitamin D. Most use ng/mL. To calculate nmol/L, multiply by 2.5.
How the body regulates vitamin D
As we’ve mentioned, the inactive form of vitamin D is first activated in the liver and then the kidneys. Supplementation tends to override this process and increase levels well beyond what time in the sun would provide.
Furthermore, taking a vitamin D supplement is not the same as vitamin D from sun exposure.
While it is possible to raise vitamin D levels to 60, 70, or 80 and above through supplementation, these high levels are rarely achieved through sun exposure – perhaps because of the regulating function of the liver and kidneys.
Furthermore, sunlight exposure produces at least one photodegradation product (5,6-trans-vitamin D) known to regulate vitamin D synthesis within the body (Gaby, 2017) which may explain why lifeguards do not typically achieve the same high vitamin D levels as individuals who aggressively supplement.
How to raise vitamin D without taking a supplement:
Magnesium – needed to make vitamin D. Most Americans are low in magnesium due to eating processed food rather than magnesium-rich foods such as leafy greens, avocados, and pumpkin seeds. Oftentimes, taking a magnesium supplement as well as eating healthy will raise vitamin D levels.
Calcium – eating calcium-rich foods increases the half-life of vitamin D.
Sun exposure – when possible, get at least 15 minutes of sun exposure to the arms and face daily. Don’t forget that vitamin D is fat-soluble meaning that sun exposure during warmer weather may help build up winter reserves.
Exercise will liberate vitamin D from fat cells
What medications deplete vitamin D?
Individuals taking the following medications should probably have their vitamin D checked regularly as well as take a supplement:
Anticonvulsants
Anti-tuberculosis drugs
Bile salt sequestrants
Statins
Hydroxychloroquine
Glucocorticoids (Gaby, 2017)
What medical conditions lower vitamin D status?
Malabsorption issues associated with GI illness or disruption such as Crohn’s disease or bariatric surgery
Liver disease
Kidney disease
Inflammation — because vitamin D is one of several markers that goes down in cases of illness or inflammation
Obesity – overweight people tend to store vitamin D in their fat
Vitamin D and obesity:
While I was studying to be a nutritionist, we were told that overweight people require high-dose vitamin D because they tend to be low. However, I’ve since learned that vitamin D is sequestered in fat tissues.
When overweight people go through dramatic weight loss, it is not uncommon for their vitamin D levels to spike. This begs the question: if overweight people need more circulating vitamin D, why doesn’t their body simply release it from fat cells?
Furthermore, obesity is considered an inflammatory state and as we’ve seen, vitamin D tends to go down with inflammation.
COVID-19
Vitamin D is widely touted as helping to improve mortality and reduce symptoms of COVID-19. It has been noted that there is an association between low vitamin D levels and adverse outcomes in hospitalized COVID-19 patients. In other words, patients with low vitamin D levels tend to fare worse. One problem with this observation is that vitamin D, like albumin, is a negative acute phase reactant, meaning it goes down when the patient is inflamed. Low vitamin D status may therefore be considered a result of inflammation and not the cause. The more relevant piece of information might be to know the patient’s baseline vitamin D status well before they get sick.
In a recent article in Nutrition Reviews, Hadizadeh notes that vitamin D deficiency is associated with an increase in pulmonary infections as well as respiratory viral infections. The highest risk was to hospitalized patients with levels less than 15. In general, supplementing with vitamin D only seemed to help the patient if he or she was truly deficient with levels below 20. However, giving COVID-19 ICU patients very high doses of vitamin D for a short duration did shorten their hospital stay (2021).
Although vitamin D supplementation is not believed to inhibit viral replication and evidence for its effectiveness is mixed (Tabatabaeizadeh 2022), it is worth considering during an acute COVID-19 infection.
Bone health
Vitamin D plays many roles in the body, including facilitating the absorption of calcium. Half of patients diagnosed with osteoporosis are deficient in vitamin D.
Studies show that levels of at least 32 are needed to maximize calcium absorption. According to research, if individuals who are low in vitamin D commit to consistently taking calcium and vitamin D, their risk of hip fractures drops significantly (Khazai, Judd & Tangricha, 2008).
While I usually recommend both calcium and vitamin D for bone health, I am conservative with the dosages. I do not subscribe to the idea that more is better. Often the opposite is true.
For example, In a recent randomized control study, about 300 healthy participants were divided into three groups, and each group was given either 400, 4,000, or 10,000 IUs of vitamin D for three years. The expectation was that the higher the dose of vitamin D, the bigger the improvement in bone mineral density, BMD. The complete opposite proved to be true!
The groups given 4,000 and 10,000 IU of vitamin D resulted in a loss of radial density. The 10,000 IU group also experienced a loss of tibia density. Furthermore, in other studies, high doses of intermittent vitamin D have been linked to an increased risk of falls, especially in frail elderly individuals.
This study and others suggest that caution is warranted when it comes to high-dose vitamin D use for bone health. Limitations of the study include the fact that participants were all healthy and did not have either osteoporosis or vitamin D levels below 30. Notably, there was also no placebo group (Burt, Billington & Rose et al., 2019).
However, a true vitamin D deficiency can cause serious problems. For example, it is a known cause of bone pain, a common complaint with severe osteoporosis (Habib, Naqi & Thillaiappan, 2020).
Vitamin D and race
When I was training to be a nutritionist, I was told that Black individuals require more vitamin D supplementation due to melanin impeding its synthesis on the skin.
In 2018, an expert panel meeting between different branches of the U.S. National Institutes of Health, including the National Institute on Minority Health and Health Disparities and the National Institute of Diabetes, convened to address the vitamin D paradox in Black Americans.
The paradox is that despite the frequency of low or even deficient vitamin D status among Black Americans, the incidence of osteoporosis and incidence of fractures was significantly lower compared to White Americans with the same low vitamin D.
While the panel was unable to explain the paradox, they recommended further investigation. The consensus view was that “Black Americans gained no skeletal benefits from high doses of vitamin D supplementation…” and that high vitamin D levels among this demographic are “almost certain to result in adverse effects” (Brown et al., 2017).
This information serves as a reminder of the biases that still exist in medical research. Often it is erroneously assumed that what is good for White clinical trial participants is good for all demographic groups.
Autoimmune diseases
The active form of vitamin D acts as a potent steroid hormone in the body. Pharmaceutical steroids are often prescribed to suppress autoimmune symptoms. Both help control symptoms of autoimmune conditions such as psoriasis, type 1 diabetes, rheumatoid arthritis, and multiple sclerosis.
Some autoimmune diseases such as type 1 diabetes and multiple sclerosis are associated with higher altitudes – regions known for low vitamin D due to reduced opportunities for sun exposure.
Very high doses of vitamin D have been given to multiple sclerosis patients, resulting in an improvement in symptoms. However, no random control trials exist to substantiate these claims. Patients given up to 50,000 IU daily were instructed to follow a strict diet and control their fluid intake (Sirbe et al, 2022).
It is hard to tease out all the ways vitamin D may reduce the symptoms of many autoimmune conditions. Vitamin D plays a role in modulating the immune system as well as suppressing inflammatory symptoms.
I usually recommend that my clients with autoimmune conditions consider vitamin D supplementation.
Cancer – breast & colon
Vitamin D supplementation is thought to help reduce the risk of certain cancers, especially breast and colon cancers. It does so by many mechanisms:
Apoptosis– which means cell suicide. Old diseased cells that stick around too long lead to cancerous growths. They need to bow out!
Antiproliferation — meaning that it can prevent a cancer from spreading!
Angiogenesis — the process by which a cancer develops its own vascular system to supply itself with blood and nutrients. Vitamin D can prevent the cancer from doing so (de La Puente-Yague et al., 2018).
Depression
People suffering from depression often have low vitamin D levels. If we think of depression as an inflammatory state, that makes sense because vitamin D is one of several blood chemistry markers that go down when the body is inflamed.
A meta-analysis of both clinical trials and observational studies revealed inconsistent results as to the benefit of supplementing with vitamin D to improve depression symptoms. Normalizing vitamin D levels did, however, help many individuals suffering from depression (Musazadeh et al., 2023).
Caution With high-dose vitamin D supplementation
If you regularly take over 2000 IU daily, consider having your calcium and phosphorus levels checked. High calcium levels are associated with increased health risks including:
Kidney stones
Kidney issues
Abnormal heart rhythm
Soft tissue calcification!
If you have high serum calcium levels, discontinue all vitamin D supplementation.
High vitamin D levels may also promote the absorption of toxic metals such as lead and mercury.
My recommendations:
The general recommendation is to supplement with between 400 and 2000 IUs of vitamin D. The potential for toxicity is believed to occur at high serum levels, especially above 150.
A Danish observational cohort study that looked at 250,000 people over five years found associations with increased mortality at both the higher and lower extremes, although the highest risks were associated with the lowest vitamin D levels (Tabatabaeizadeh 2022).
Ideally, I like to test vitamin D levels before making a supplement recommendation. For clients with bone health concerns, I like to see levels between 30 and 40. Any higher may lead to the suppression of osteoblasts, the bone-building cells.
For clients with cancer or autoimmune issues, I usually recommend at least 40. Vitamin D also helps protect the body during chemotherapy (Sirbe et al., 2022).
As we’ve seen, age and race also factor into making decisions about whether or not to supplement with vitamin D.
Ideally, you should consult a nutritionist to see what is right for you!
Disclaimer
The included information is not meant to or should not be used to replace or substitute medical treatment, recommendations, or the advice of your physician or health care provider. The information contained within is strictly for educational purposes and is based on evidence-based nutrition. If you believe you have a medical problem or condition, please contact your physician or healthcare provider.
References:
Tabatabaeizadeh S. A. (2022). Zinc supplementation and COVID-19 mortality: a meta-analysis. European journal of medical research, 27(1), 70. https://doi.org/10.1186/s40001-022-00694-z
Burt, L. A., Billington, E.O. & Rose, M.S. (2019) Effect of high-dose vitamin D supplementation on volumetric bone density and bone strength: a randomized control study. JAMA Network.https://jamanetwork.com/journals/jama/fullarticle/2748796
Brown, L.L., Cohen, B., Tabor, D., Zappala, G., Maruvada, P., & Coates, P.M. (2018. The vitamin D paradox in Black Americans: a systems-based approach to investigating clinical practice, research, and public health — expert panel meeting report. BMC proceedings, 12 (Suppl 6), 6 https://doi.org/10.1186/s12919—018-0102-4
de La Puente-Yagüe, M., Cuadrado-Cenzual, M. A., Ciudad-Cabañas, M. J., Hernández-Cabria, M., & Collado-Yurrita, L. (2018). Vitamin D: And its role in breast cancer. The Kaohsiung journal of medical sciences, 34(8), 423–427. https://doi.org/10.1016/j.kjms.2018.03.004
Gaby, A. (2017). Nutritional Medicine: Second Edition. Fritz Perlberg Publishing: Concord, NH.
Habib, A. M., Nagi, K., Thillaiappan, N. B., Sukumaran, V., & Akhtar, S. (2020). Vitamin D and Its Potential Interplay With Pain Signaling Pathways. Frontiers in immunology, 11, 820. https://doi.org/10.3389/fimmu.2020.00820
Khazai, N., Judd, S. E., & Tangpricha, V. (2008). Calcium and vitamin D: skeletal and extraskeletal health. Current rheumatology reports, 10(2), 110–117. https://doi.org/10.1007/s11926-008-0020-y
Mangin, M., Sinha, R., & Fincher, K. (2014). Inflammation and vitamin D: the infection connection. Inflammation research: official journal of the European Histamine Research Society ... [et al.], 63(10), 803–819. https://doi.org/10.1007/s00011-014-0755-z
Musazadeh, V., Keramati, M., Ghalichi, F., Kavyani, Z., Ghoreishi, Z., Alras, K. A., Albadawi, N., Salem, A., Albadawi, M. I., Salem, R., Abu-Zaid, A., Zarezadeh, M., & Mekary, R. A. (2023). Vitamin D protects against depression: Evidence from an umbrella meta-analysis on interventional and observational meta-analyses. Pharmacological research, 187, 106605. https://doi.org/10.1016/j.phrs.2022.106605
Sîrbe, C., Rednic, S., Grama, A., & Pop, T. L. (2022). An Update on the Effects of Vitamin D on the Immune System and Autoimmune Diseases. International journal of molecular sciences, 23(17), 9784. https://doi.org/10.3390/ijms23179784