This study seeks to determine if vitamin D3 absorption in healthy adults will be enhanced in the presence of a meal and if the enhancement will be greater when the meal is low as opposed to high in fat content. The enhancement will result from increased vitamin D absorption. The investigators will test this hypothesis by pursuing the following aims in a 3-mo trial in which up to 70 healthy men and women will be randomized to one of the following meal conditions under which they will take a monthly oral dose of 50,000 IU of vitamin D3: no meal (fasting), a low fat meal, or a high fat meal. The Primary Aim is to identify the meal condition (fasting, low-fat, or high-fat meal) under which the 25OHD3 response to supplemental vitamin D3 is greatest and most consistent. The Secondary Aim is to determine whether vitamin D3 absorption is affected by the meal condition and to determine whether the absorption of vitamin D3 predicts the longer-term 25OHD3 response to supplementation.

Vitamin D supplements are increasingly recommended to curb widespread deficiency. Decreasing the variability in 25OHD responses to supplemental vitamin D would make the supplementation process more predictable, and thereby reduce the number of 25OHD measurements and dose adjustments that are needed to achieve the targeted 25OHD level. This study seeks to identify potential sources of variability in the 25OHD3 response to supplemental vitamin D3 that are plausible based on rat studies, but have not been explored in humans. The investigators hypothesize that the serum 25OHD3 response to supplemental vitamin D3 in healthy adults will be enhanced in the presence of a meal and the enhancement will be greater when the meal is low as opposed to high in fat content. The enhancement will result from increased vitamin D absorption. The investigators will test this hypothesis by pursuing the following aims in a 3-mo trial in which up to 70 healthy men and women will be randomized to one of the following meal conditions under which they will take a monthly oral dose of 50,000 IU of vitamin D3: no meal (fasting), a low fat meal, or an iso-caloric high fat meal. Serum 25OHD3 will be measured at baseline and after 1 and 3 mo. A serum vitamin D3 absorption test will be performed in each subject after the first dose of vitamin D. The Primary Aim is to identify the meal condition (fasting, low-fat, or high-fat meal) under which the 25OHD3 response to supplemental vitamin D3 is greatest and most consistent. The Secondary Aim is to determine whether vitamin D3 absorption is affected by the meal condition and to determine whether the absorption of vitamin D3 predicts the longer-term 25OHD3 response to supplementation.

Inclusion Criteria:

• Ages 50 to 69
• BMI ≥ 18.5 and ≤ 27.9 kg/m2
• those taking ≤ 400 IU/day of vitamin D3 and ≤ 1000 mg calcium/day
• those who participate must agree not to change their dietary or supplemental vitamin D or calcium intake during the study
• no use of tanning salons
• no travel south of latitude 34 degrees north during the study

Exclusion Criteria:

General:

1. A screening 25OHD level ≤8 or ≥ 25 ng/ml
2. An abnormal serum calcium (reference range is 8.3 -10.2 mg/dl)
3. A screening spot urinary calcium:creatinine ratio > 0.325
4. Greater than 2 drinks of alcohol a day.
5. BMI <18.5 and >27.9 kg/m2
6. Menses within the last year (women)
7. Age <50 and > 69 years
8. Allergy to egg
9. A blood donation in the last 2 months (increases likelihood of anemia)
10. Non-English speaking subjects will not be enrolled.
11. Other abnormalities in screening labs, at the discretion of the study physician (PI)

Medications:

1. Subjects must agree not to take more than 400 IU per day of vitamin D as supplement or cod liver oil during the study
2. Topical vitamin D preparations
3. Oral estrogen or estrogen patch use in the last 6 months
4. Regular antacid use (>2 times per week)
5. Sucralfate
6. Acarbose/miglitol
7. PPIs - prescription: lansoprazole (Prevacid), omeprazole (Prilosec and Zegerid), esomeprazole (Nexium), rabeprazole (Aciphex), pantoprazole (Protonix); over-the-counter: lansoprazole (Prevacid 24), omeprazole (Prilosec OTC), zegerid OTC (Equate), omeprazole magnesium
8. H2 blockers - prescription: cimetidine (Tagamet), famotidine (Pepsid), nizatidine (Axid), rantidine hydrochloride (Zantac), dexlansoprazole (Kapidex); over the counter: cimetidine (Tagamet-HB, Equate), famotidine (Pepcid-AC, Pepcid Complete), rantidine hydrochloride (Zantac, Wal-Zan, Equate)
9. Drugs that alter fat and cholesterol handling - xenical and alli (Orlistat), cholestyramine (Questran, LoCholest, Prevalite), Zetia
10. Drugs that alter 25OHD metabolism - Antiseizure drugs phenobarbitol and phenytoin (Dilantin), oral glucocorticoids
11. Calcium supplement use >1000 mg/day

Diseases:

1. Active parathyroid disease
2. Sarcoidosis
3. Peptic ulcers or esophageal stricture
4. Active malignancy (other than basal cell cancer of the skin) or cancer therapy in the last year
5. Advanced kidney disease (creatinine clearance <30 ml/min calculated from serum creatinine with use of the Modification of Diet in Renal Disease (MDRD) Study equation
6. Kidney stones in the last 5 years.
7. Liver disease
8. Zollinger-Ellison syndrome
9. Known achlorhydria or small bowel overgrowth
10. Malabsorption
11. Diseases associated with fat malabsorption - liver disease, cystic fibrosis, Celiac disease, bariatric surgery, Scleroderma, Crohn's, prior surgery involving the stomach or small bowel (appendectomy okay), gall stones or prior gall bladder surgery, pancreatitis