If you missed Vitamin D (Part I), start there and then read on. 

What is Vitamin D used for?

Vitamin D is used for phosphate deficiency diseases such as hypophosphatemia. As discussed above, vitamin D plays a role in phosphorus regulation, so supplementing with Vitamin D and phosphate is effective for treating bone disorders in people with this disease. Fanconi syndrome, a disease that affects phosphate levels, can also be helped by taking Vitamin D. 

Vitamin D may be helpful in psoriasis due to its role of proliferation and maturation of keratinocytes and anti inflammatory activity. Furthermore it has been investigated that problems with the VDR are associated with psoriasis. It has been used both topically and internally for this condition. 

Vitamin D can be helpful for thyroid conditions including those that result from decreased vitamin D levels leading to overactive parathyroid glands or those that cause low calcium levels.

Vitamin D can be helpful for fall prevention due to its strengthening effects on the bones and muscles, it can help with muscle weakness and pain due to vitamin D deficiency, and osteoporosis. 

Vitamin D may be supportive for asthma because it may help reduce inflammation and decrease asthma severity. It also may reduce inflammation and help prevent and treat autoimmune diseases. Through the VDR, vitamin D helps modulate the immune system which may suggest its role in autoimmune diseases. Additionally, some research has shown a potential link between VDR polymorphisms and autoimmune diseases. 

 

 

 

Vitamin D can be helpful for people with chronic kidney disease, particularly for their bone health. Vitamin D has also been studied for its use for cancer prevention. Vitamin D intake with or without calcium has been studied for colorectal, cervical, breast, and prostate cancer. A reduced risk of colorectal cancer has been shown with vitamin D supplementation. 

Vitamin D can be used to improve cognition or prevent cognitive decline such as in Alzheimer’s disease (AD). Studies have shown that higher blood levels of vitamin D3 are associated with better mental performance in people with AD. Vitamin D may be helpful in Alzheimer’s because it has neuro protective effects through regulating nerve growth and neurotrophic factors such as nerve growth factor, decreasing L-type calcium channel expression, and regulating the toxicity of reactive oxygen species and nitric oxide synthase.

Additionally, vitamin D showed a lower accumulation of AB42 by enhancing its phagocytosis and amplifying brain-to-blood amyloid beta efflux transport at the blood-brain barrier (BBB), leading to fewer amyloid plaques. Once again looking at the VDR, studies have shown an association between VDR gene polymorphisms and cognitive decline in Alzheimer’s. Vitamin D deficiency has also been linked with increasing hypertension, hyperlipidemia, myocardial Infarction (MI), and stroke, which are also risk factors for AD so Vitamin D may be preventative for Alzheimer’s in these ways as well. 

Vitamin D can also be helpful for mood disorders. As discussed above, Vitamin D helps with the health of the gut and microbiome which in turn supports a healthy mood. It may support mood disorders such as seasonal affective disorder, PMS, and depression. 

 

 

 

Vitamin D is also helpful for preventing and supporting osteoporosis. It helps with calcium absorption and maintaining good levels of calcium in the body without having to take from the bones as discussed above. 

Vitamin D may be supportive for type 2 diabetes due to its effect on insulin. Additionally, vitamin D3 may help normalize diabetes-induced alterations in cholinergic insulin receptors  and vitamin D receptor and may also support normal glucose transport and utilization. 

 

 

 

Vitamin D may also support normal cholesterol levels. Studies have shown that it may be helpful in reducing triglycerides, reducing LDL, and improving HDL levels. 

Vitamin D may be useful in treating and preventing fractures, fibromyalgia, hypertension, inflammatory bowel disease, oral health of the teeth, and atopic eczema. 

 

What are the available forms of Vitamin D?

The available forms of vitamin D mainly come in the form of Vitamin D3. There are options for liquid form, capsule form, and vegan options as well. 

For D3, you can get it at a potency of 400 IU by Pure, 1000 IU by Ortho Molecular, Thorne, or Pure, 2000 IU by Xymogen, 5000 IU by Xymogen, Thorne, or Ortho Molecular, or 10,000 IU Thorne.

You can also get D3 with K2, which is recommended especially if you are taking 5,000+ IU of D3 because while D3 helps absorb calcium in the intestine, K2 directs the calcium from the blood into the bones. For combined options, there is a 1000 IU D3 and 120 mcg K2 by Bioclinic Naturals, a 5000 IU D3 and 90 mcg K2 by Xymogen, a 5000 IU D3 with 45 mcg K2 by Ortho Molecular, a 10000 IU D3 with 45 mcg K2 by Xymogen, and K2 D3 Max Xymogen which has 5,000 IU D3 and 180 mcg K2. For other combination options, try Seeking Health, Protocol, and Vital Nutrients. 

There is also a nanoemulsified pump option: Nanoemulsified  Vitamin D3-K2 Quicksilver to feature quick and high absorption, which features 2500 IU D3 with 90 mcg K2. 

For liquid, there is a 1000 IU liquid Vitamin D by Pure, Xymogen, and Ortho Molecular. For a liquid D3 and K2 combination, Thorne has a 1000 IU D3 with 200 mcg K2, and Ortho Molecular has a 1000 IU D3 and 10 mcg K2. 

For a vegan option derived from algae, try Vegan Vitamin D Pure. 

What are food sources of Vitamin D?

There are very few food sources that contain significant amounts of vitamin D. Foods that contain a significant amount of vitamin D include fish, particularly salmon, sardines, herring, and mackerel, meat, milk, eggs, butter, liver, and mushrooms. 

 

 

 

What are contraindications of Vitamin D?

Vitamin D may interact with aluminum, calcipotriene, digoxin, diltiazem, orlistat, thiazide diuretics, steroids, stimulant laxatives, verapamil, lipid-lowering drugs, glucocorticoids, calcium-channel blockers, topical anti-fungal agents, anticonvulsants, antituberculosis medications, anti-rejection medications, and HAART (AIDS treatment). 

 

What are the side effects of taking Vitamin D?

Some possible side effects of taking larger amounts of vitamin D are upset stomach and vomiting, weight loss and not wanting to eat, muscle weakness, not being able to think clearly or quickly, heart rhythm issues, and kidney stones and kidney damage. Other possible side effects include excessive thirst, diarrhea, nausea, weakness, and headaches. Taking too much vitamin D could also contribute to excess calcium in the arteries and soft tissues, which is why it is recommended to take Vitamin K2 to help direct that calcium into the bones when taking higher amounts of D3. 

 

 

 

References

Aggeletopoulou, I. et al. Vitamin D and Microbiome: Molecular Interaction in Inflammatory Bowel Disease Pathogenesis. The American Journal of Pathology, 193(6), 656-668.

https://ajp.amjpathol.org/article/S0002-9440(23)00055-X/fulltext 

Association for the Advancement of Restorative Medicine. Vitamin D. https://restorativemedicine.org/library/monographs/vitamin-d/ 

Barrea, L. et al. (2017). Vitamin D and its role in psoriasis: An overview of the dermatologist and nutritionist. Rev Endocr Metab Disord., 18(2), 195-205.  https://pmc.ncbi.nlm.nih.gov/articles/PMC5486909/ 

Chakkera, M. (2022). The Efficacy of Vitamin D supplementation in patients with Alzheimer’s disease in preventing cognitive decline: A systematic review. Cureus 14(11). https://pmc.ncbi.nlm.nih.gov/articles/PMC9771092/ 

Chen, H. et al. (2025). Higher dietary vitamin D intake influences brain and mental function in elderly Americans: a cross-sectional analysis. Frontiers, 12. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1564568/full 

Gbadamosi, I. et al. (2024). Vitamin D attenuates monosodium glutamate-induced behavioural anomalies, metabolic dysregulation, cholinergic impairment, oxidative stress, and astrogliosis in rats. NeuroToxicology 103, 297-309. https://www.sciencedirect.com/science/article/abs/pii/S0161813X24000706#:~:text=Furthermore%2C%20Vitamin%20D%20has%20been,and%20cerebellum%20of%20Wistar%20rats. 

Haas, E.M. (2006). Staying Healthy with Nutrition: The Complete Guide to Diet and Nutritional Medicine: 21st Edition.Ten Speed Press. 

Hechtman, Leah. (2019). Clinical Naturopathic Medicine: Second Edition. Elsevier. 

Higdon, Jane. (2000). Vitamin D. Linus Pauling Institute Micronutrient Information Center. https://lpi.oregonstate.edu/mic/vitamins/vitamin-D 

Kumar, P.T. et al. (2011). Vitamin D3 restores altered cholinergic and insulin receptor expression in the cerebral cortex and muscarinic M3 receptor expression in pancreatic islets of streptozotocin induced diabetic rats. The Journal of Nutritional Biochemistry, 22(5), 418-425.. https://www.sciencedirect.com/science/article/abs/pii/S0955286310000835#:~:text=Vitamin%20D3%20restores%20altered%20cholinergic%20and%20insulin,pancreatic%20islets%20of%20streptozotocin%20induced%20diabetic%20rats.&text=In%20conclusion%2C%20vitamin%20D3%20shows%20a%20potential,glucose%20transport%20and%20utilisation%20in%20the%20cortex. 

Malaguarnera, Lucia. (2020). Vitamin D and microbiota: Two sides of the same coin in the immunomodulatory aspects. International Immunopharmacology, 79.

https://www.sciencedirect.com/science/article/abs/pii/S1567576919324105 

Schaefer, Anna. (2025). What’s the relationship between Vitamin D and cholesterol? Healthline. https://www.healthline.com/health/high-cholesterol/vitamin-d-relationship#vitamin-d-and-cholesterol 

Yang, Cheny-Yen. et al. (2013). The Implication of VItamin D and Autoimmnity: a Comprhensive Review. Clin Rev Allergy Immunol, 45(2), 217-226.  https://pmc.ncbi.nlm.nih.gov/articles/PMC6047889/