Obstacles to Vitamin D Sufficiency- Why It Can Be Hard to Achieve

Chris D. Meletis, N.D.

It happens more often than I would expect in clinical practice: a patient is faithfully taking their vitamin D, yet still not achieving the individual vitamin D levels set for their health goals. In reality, vitamin D sufficiency isn’t always so easy to reach. The reason why our patients often fall short of optimal vitamin D levels is that they are confronted with a variety of factors that interfere with vitamin D absorption.  

This article will address those factors that stop our patients from meeting targeted vitamin D goals and provide an easy solution to enhance the absorption of a nutrient critical to cardiovascular, neurocognitive, cellular, bone, and immune health.^1-3

Symptoms of Low Vitamin D

Vitamin D insufficiency and deficiency aren’t always obvious, at least not at first. Here are some symptoms I see in clinical practice and in the research that correlate with low vitamin D levels. ^4-6

• Bone pain
• Changes in mood, such as depression and irritability
• Fatigue
• Frequent fractures
• Getting sick often (a sign of a weakened immune system)
• Muscle weakness, cramps, or aches
• Sleep problems

Under Recognized Causes of Vitamin D Insufficiency and Deficiency

Digestive and Gastrointestinal Causes

These affect how vitamin D (a fat-soluble vitamin) is released from food and absorbed in the intestines: ⁷

• Celiac disease – damage to intestinal villi reduces nutrient uptake.
• Crohn’s disease – inflammation can affect absorption in the small intestine.
• Ulcerative colitis – can reduce fat absorption during flares.
• Short bowel syndrome – less surface area for absorption after surgery.
• Pancreatic insufficiency (e.g., cystic fibrosis, chronic pancreatitis) – poor fat digestion means vitamin D can’t be freed from food.
• Bile duct obstruction or cholestatic liver disease – bile salts are essential for emulsifying fat; without them, vitamin D uptake is reduced.

Dietary and Lifestyle Factors⁷

• Low dietary fat intake – vitamin D needs fat for absorption.
• Strict vegan diet without supplementation – vitamin D2 from plants is less efficiently converted to active D.
• Low sun exposure – no synthesis in skin.
• Dark skin pigmentation – melanin reduces UVB-driven vitamin D synthesis.

Increased Needs or Losses⁷

• Obesity – vitamin D is sequestered in fat tissue, making it less available in circulation.
• Pregnancy or lactation – increased demand.
• Aging – skin is less efficient at synthesizing vitamin D.

Medications and Supplements That Cause Low Vitamin D

Several medications can block the absorption of vitamin D or lower levels via other mechanisms. Some dietary supplements can have the same effect. This table lists the primary offenders:^7-9

Medication Category	Drug Examples
Anti-seizure medications	Phenytoin, phenobarbital, carbamazepine, valproic acid
Blood pressure medicines	Nifedipine and spironolactone
Cancer treatments	Taxol
Estrogen-blocking drugs for breast cancer	Tamoxifen and fulvestrant
Medicines for infections	Isoniazid for tuberculosis, ritonavir for HIV, and clotrimazole for fungal infections
Steroids	Prednisone, dexamethasone, and methylprednisolone
Supplements	St. John’s wort and kava kava
Cholesterol-lowering drugs	Cholestyramine and colestipol
Laxatives
Weight loss drugs	Orlistat

An Easy Way To Improve Vitamin D Absorption

VESIsorb® technology, is an ideal way to ensure that patients are absorbing an optimal amount of vitamin D3, even in the face of a host of factors that interfere with vitamin D absorption. VESIsorb® delivery system offers enhanced absorption by promoting the ability for vitamin D to dissolve readily in an aqueous environment. VESIsorb® eliminates the need for taking vitamin D3 with a fatty meal. VESIsorb® provides a self-assembling colloidal system that forms evenly dispersed fluid droplets upon contact with water in the GI tract. These droplets have a mean diameter of less than 100 nanometers, allowing the bioactive to cross the water layer of the GI tract for absorption.¹⁰

 

References:

1. Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med. 1997;337(10):670-676.
2. Garland CF, Garland FC, Gorham ED, et al. The role of vitamin D in cancer prevention. Am J Public Health. 2006;96(2):252-261.
3. Giovannucci E, Liu Y, Hollis BW, Rimm EB. 25-hydroxyvitamin D and risk of myocardial infarction in men: a prospective study. Arch Intern Med. 2008;168(11):1174-1180.
4. Abukhalil AD, Falana H, Hamayel R, et al. Vitamin D Deficiency Association with Comorbid Diseases in Palestine: “A Cross-Sectional Observation Study”. Int J Gen Med. 2022;15:8033-8042.
5. Al Zarooni AAR, Nagelkerke N, Al Marzouqi FI, Al Darmaki SH. Risk factors for vitamin D deficiency in Abu Dhabi Emirati population. PLoS One. 2022;17(2):e0264064.
6. Sabião TDS, Menezes-Júnior LAA, Batista AP, et al. Exploring the interaction between vitamin D pathway gene polymorphisms, vitamin D status, and depression: A population-based study. Nutrition. 2025;137:112802.
7. Vitamin D Deficiency. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency. Published 2022. Accessed August 13, 2025.
8. Gröber U, Kisters K. Influence of drugs on vitamin D and calcium metabolism. Dermatoendocrinol. 2012;4(2):158-166.
9. Jung JW. Drug-Induced Vitamin Deficiency. Ann Clin Nutr Metab. 2022;14(1).
10. Knaub K, Sartorius T, Dharsono T, Wacker R, Wilhelm M, Schön C. A Novel Self-Emulsifying Drug Delivery System (SEDDS) Based on VESIsorb(®) Formulation Technology Improving the Oral Bioavailability of Cannabidiol in Healthy Subjects. Molecules. 2019;24(16).