Brief Answer:
Infection, foods, supplements,GI bleeding...see details below...

Detailed Answer:
Hi,

I understand your concern.

Your case:
- 67 years old male
- symptoms: black stools along with diarrhea

Diarrhea is a sign of possible inflammation/infection of bowels.
Black stool could be related to:
- foods you might have consumed (e.g. dark leaves, iron fortified foods)
- supplements you might take (e.g. iron supplements)
- pathologies of upper GI tract causing bleeding (e.g. ulcer, tumors, etc.)

These are general information only.
To be more specific, I need to have a few more information regarding your current health status:
- are you having problems like: pain? burning sensation in the throat? stomach? after eating?
- do you suffer of any chronic illness: diabetes? heart disease? liver/kidney problems?
- are you taking any medication on regular basis: blood thinners? any supplement?
- personal history of anemia? or gastrointestinal bleeding?
- any examination so far?

Thank you!
Dr.Albana

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