From the Guidelines
Cortisol levels can be measured after food intake, but it is generally recommended to have your cortisol levels measured in a fasting state for the most accurate results. The impact of food intake on cortisol levels is usually minimal, but it can temporarily alter hormone levels in your bloodstream 1. For salivary cortisol tests, it's essential to avoid eating, drinking anything besides water, brushing teeth, or using tobacco products for at least 30 minutes before sample collection.
Key Considerations
- For 24-hour urine cortisol tests, you can eat normally throughout the collection period.
- Cortisol follows a natural daily rhythm, being highest in the morning and lowest at night, so the timing of your test is actually more important than your food intake.
- If your doctor has given you specific instructions about eating before your cortisol test, you should follow those guidelines as they may be tailored to your particular situation.
Evidence-Based Recommendations
- A study published in The Lancet Diabetes and Endocrinology in 2021 1 provides guidance on the diagnosis and management of Cushing's disease, including the use of cortisol testing.
- The study highlights the importance of considering factors that may affect cortisol levels, such as concomitant medications and decreased corticosteroid binding globulin (CBG) levels.
- Measuring dexamethasone concomitantly with cortisol can reduce the risk of false-positive results 1.
From the Research
Cortisol Levels and Food Intake
- Cortisol levels can be measured after food intake, as studies have investigated the effect of food on cortisol levels and hydrocortisone replacement therapy 2.
- One study found that food intake delayed the time to reach a clinically significant plasma concentration of cortisol (>200 nmol/l) by 28 and 9 minutes based on LC-MS/MS and immunoassay, respectively 2.
- The same study showed that plasma cortisol levels remained above 200 nmol/l for around 6 hours after administration of a 20 mg dual-release hydrocortisone tablet, and all plasma concentrations 18-24 hours after intake were below 50 nmol/l 2.
Hydrocortisone Replacement Therapy
- Hydrocortisone replacement therapy aims to replicate the physiological concentrations of cortisol, but the pharmacokinetics of oral immediate-release hydrocortisone make it impossible to fully mimic the cortisol rhythm 3.
- Studies have investigated the use of modified-release hydrocortisone formulations to mimic the normal circadian rhythm of circulating cortisol 4, 5.
- These formulations have shown promise in reproducing the normal early morning rise in serum cortisol and providing a more physiological plasma concentration-time profile of hydrocortisone 5, 2.
Cortisol Measurement
- Cortisol levels can be measured using various methods, including LC-MS/MS and immunoassay 2.
- Studies have used these methods to investigate the pharmacokinetics of hydrocortisone and the effect of food intake on cortisol levels 2.
- The measurement of cortisol levels is important for monitoring treatment and dose titration in patients with adrenal insufficiency 3.