Understanding Bioavailability - Part 1 : External, Inborn & Health Related Factors

Bioavailability refers to how much of a substance is absorbed into the bloodstream and made available for the body to use after uptake. In other words, it’s not just about what you consume, but how much your body can actually absorb and utilize.

A wide range of factors can influence this process. Because there’s so much to consider, we’ve divided this discussion into two parts. This first article looks at external influences, inborn factors, and health-related complications, while the next will explore additional dietary factors that affect absorption.

External Factors

Several external factors affect the bioavailability of any given substance. These include:

• The form the substance takes: for example whether the substance is a liquid or powder.
• The method of uptake: meaning, whether the substance is taken orally, topically, intravenously, etc.
• Whether a substance is taken with food, drink, or on an empty stomach: one or the other may be preferred depending on the substance.
• Temperature & pH: some substances like enzymes may be less active at a certain pH or temperature. For example, enzymes in the stomach that break down proteins and fats require a low pH for optimal functioning. 
• Solubility & digestibility: water-soluble substances are more easily absorbed than fat-soluble substances, and certain substances may be trapped within something indigestible such as the fibrous chitin in the cell walls of mushrooms. Cooking and fermentation can help release these nutrients. For example, valerian root taken as a tea after steeping (hot water extraction) is typically more effective than when taken as a capsule.
• The presence of other substances: some substances such as iron and calcium can compete for absorption when taken in large quantities.  On the other hand, some substances such as black pepper extract and lecithin can aid in the absorption of certain other ingredients. Another example is bromelain aiding quercetin absorption. Certain medications that affect digestion can also decrease overall nutrient absorption.

Beyond the above-listed factors, two critical things to consider concerning bioavailability are inborn factors and health complications.

Inborn Factors

Inborn factors such as gender, genetics, and age can impact nutrient absorption.

Health Complications

The following health conditions have a direct impact on nutrient absorption.

1. Hypothyroidism: Slows metabolism and reduces digestive function, leading to decreased enzyme and acid production and reduced absorption of nutrients like iron, calcium, and B vitamins. 
   
2. Hyperthyroidism: Increases metabolism and digestive activity, potentially enhancing nutrient absorption, but can also lead to malabsorption issues if gastrointestinal symptoms get out of hand.
   
3. Diabetes: Both type 1 and type 2 diabetes can affect nutrient metabolism and absorption due to insulin-related issues, leading to nutrient imbalances and deficiencies.
   
4. Cushing's syndrome: High cortisol levels can increase blood sugar, promote muscle breakdown, and decrease protein absorption.
   
5. Estrogen imbalances: Affect calcium metabolism, potentially impacting absorption and utilization, leading to bone health issues.
   
6. Adrenal insufficiency: Hormonal imbalances can affect nutrient absorption and electrolyte balance.
   
7. Growth hormone disorders: Impact nutrient metabolism, particularly during growth and development stages.
   
8. Celiac disease: Autoimmune disorder causing intolerance to gluten, leading to malabsorption of nutrients, especially iron, calcium, and B vitamins.
   
9. Inflammatory bowel disease (IBD): Chronic inflammation of the digestive tract impairs nutrient absorption and leads to deficiencies.
   
10. Irritable bowel syndrome (IBS): Alters gut motility and absorption, causing issues like diarrhea, constipation, and bloating.
    
11. Gastroesophageal reflux disease (GERD): Chronic acid reflux damages the esophageal lining, impairing nutrient absorption.
    
12. Gastric bypass surgery: Alters digestive tract, impacting nutrient absorption, and necessitating lifelong supplementation.
    
13. Gastrointestinal infections: Disrupt normal digestive function, leading to malabsorption, particularly during diarrheal illnesses.
    
14. Pancreatic insufficiency: Inadequate production of digestive enzymes impairs nutrient absorption, especially fats and fat-soluble vitamins.
15. Small intestinal bacterial overgrowth (SIBO): Excessive bacterial growth interferes with nutrient absorption, causing symptoms like bloating and diarrhea.

This is far from an exhaustive list, and many other conditions can affect individualized nutrient bioavailability. 

Conclusion

This concludes Part 1 of our article on bioavailability. In Part 2 we’ll examine anti-nutrients and the food matrix.